At its core, conversion requires that the ger (convert) willingly, and without ulterior motive, accept kabbalat ol mitzvot - the acceptance of the mitzvot (commandments) upon him or herself. The classical sources say that, once this intent has been shown, he/she has to be taught a few "light" commandments and a few "heavy" commandments, and then they are ready to convert.

 

In modern times, this early stage has become quite involved. Although it varies greatly, based on the Rabbi, and the specifics of the case, conversion often takes a minimum of a year, and often quite longer. It involves education about the basic tenents and practices of Judaism, a chance to learn first-hand about Judaism by participating in Jewish life (one of the reasons for the year of study is to ensure that the ger has experienced all of the Jewish holidays, personally), as well as a chance to explore larger philosophical issues (such as theology) with the sponsorong Rabbi.

 

In Reform Judaism, there is also a major difference with the idea of kabbalat ol mitzvot. Unlike Orthodox and Conservative Judaism, Reform Judaism doesn't demand obedience of all Jewish laws; it instead insists on learning about those laws, and being guided by them. Most Reform Rabbis would insist on some serious level of observance before they would convert someone, but few would demand that any specific practices, such as keeping kosher, be adhered to.

 

The details of this preparatory period vary widely from movement to movement and, especially, from Rabbi to Rabbi. the only way to really get an idea of what is involved is to make an appointment with a Rabbi and ask him or her.

 

Once the candidate is ready for conversion, they are brought before a beit din, a Rabbinical court. This beit din ensures that the ger is ready for conversion (both in terms of sincerity, as well as general preparation for a Jewish life), and then (hopefully) accepts the ger ito the Jewish world. But, the ger is still not a Jew, at this point.

 

Once accepted by the beit din, the ger becomes a Jew by undergoing a ritual or two. Men are required to have a brit milah - a ritual circumcision. Men who were already medically circumcised instead go through hatafat dam brit - the ritual drawing of a drop of blood from the circumcision site. Both of these rituals officially bind the man to the brit (covenant) with God. The final stage of conversion, for men and women, is immersion in a mikvah - a ritual bath. Once that ritual is performed, the ger is now a Jew!

 

Again, in the Reform movement, standards vary. Some Rabbis insist on brit milah or hatafat dam brit and mikvah; some don't. The only way to be sure is to find a Rabbi, and ask!

Three times, the Torah tells us not to eat a kid (a baby goat, not a child!) which has been boiled in it's mother's milk. [An important aside: There are some tricky translation issues here. "Milk" may actually be "fat" or, more precisely, one particular kind of fat. "Boil" may be "seeth," which is different. In the end, these issues probably don't matter, because regardless of what the original language may have been, the law developed into the concrete system which we have today]. The Rabbis of old understood this to be a general injunction to not eat an animal with any milk from its mother.

 

Very quickly, this law expanded - just to be safe (to prevent accidental mixing), we shouldn't eat meat with the milk of any animal of that species, not just the mother (how can you be sure which animal this milk came from?), and then, for the same reasons, to any milk from any animal. Even chicken (and other birds), which don't have milk, came under this restriction (although, there was much more debate about this in Talmudic times - roughly 2000 years ago), because of the ease of confusion (if you'll eat one meat with milk, it's easy to accidentally eat another meat with milk, too).

 

This is all a classic case of "building a fence around the Torah." We enact extra laws and regulations to make sure that we don't even come close to violating important laws. Eventually, the laws expand so much that the sages of old referred to the laws of kashrut as a mountain suspended by a thread - a huge amount of law, based on the tiniest bit of textual grounding.

 

My own opinion is that the origin of these laws is not what's really important. Whereever these laws came from, they have evolved over the centuries into a distinctively Jewish way of eating. I don't avoid mixing meat and milk because the Torah says, "don't boil a kid in it's mother's milk" per se. I avoid mixing meat and milk because that's a Jewish dietary practice. I want to eat like a Jew, and this is one of the ways in which I do so!

My colleagues have answered this question very well, so I don't have too much to add, except for my agreement.

 

Since it was brought up, I know that there are some Reform Rabbis who will convert a person into Judaism, regardless of what they do or don't believe. Others would say that a person must believe in God, although what it means to believe in God are open to an incredibly wide range of interpretations (most people who say they are atheists are actually agnostic - they just don't believe in a particular image of God which they had been given as authoritative).

 

As one of the other respondents said, Judaism certainly affirms the existence and oneness of God, even though it never really demands belief, per se. Or, in the words of one of my Rabbis, "what makes you think God cares if you believe in God or not?"

 

Rabbi Levy gave an excellent overview of the legal tradition behind the banning of chicken and dairy. In addition, there is another perspective from which we can answer this question.

 

In a wonderful article entitled, "Locusts, Giraffes, and the Meaning of Kashrut" Meir Soloveichik argues pursuasively that people often go wrong when the look for the meaning behind the laws of kashrut. In essence, he says that the individual laws don't contain any meaning or rationale. But, taken together, they form a distinctively Jewish way of eating, and that is the value of the dietary system. We could just as easily eat only land animals which don't have cloven hoofs and chew their cud; so long as we're all agreeing to eat in a similar way (or, so long as God commanded us to eat that way), then we're doing the right thing. [Solevichik certainly wasn't the first to argue this, but he does so very well!]

 

My favorite metaphor is that it's a bit like wearing the colors of your favorite sports team. It's not the colors themselves which matter, it's the symbol of team affiliation - e.g. "all fans of this team wear red" - that really matters.

 

So, while the "where did this law come from" version of this answer is very interesting, on some level, to me, it misses the point. I don't eat dairy with chicken because that's part of "Jewish eating." Even if I believe, as I do, that it was somewhat unecessary to include that restriction in the larger law (especially since some Talmudic Rabbis didn't agree with it, as Rabbi Levy pointed out), I have to admit that Chicken Parmesian just isn't kosher. That seems to be one of the few things that most Jews can agree on! So, my decision to not eat it isn't so much about the Talmudic arguments, as it is about deciding to eat Jewishly.