There is no Scriptural Prohibition against lesbianism in the Torah, but there is definitely a law against it. The sin is not the same as gay relations, and in fact is a much lesser sin, but it is still against the Orthodox Jewish Laws.

The Talmud quite clearly lays out what the guidelines for sexual intimacy are, and the fact that it is not between a man and a women quite clearly places it in the realm of forbidden acts. It is listed specifically as a sin that receives Makkos, or Lashes. This places it in the same category (in terms of punishment) as intimacy before marriage (such as kissing a member of the opposite sex) or plowing in a graveyard (planting crops over bodies is discouraged). Obviously these are not "top-tier" sins, but they are not negligible either.

The most important idea in Judaism pertaining to this issue is the concept (that Christianity stole intact) of hating the sin, but loving the sinner. Obviously, everybody sins, and it is ridiculous to say that lesbians should be stigmatized any more than teenagers that are caught making out somewhere, but unfortunately, people are jerks, and societal mores have influenced the degree of stigmatization that a particular sin has.

Of course, it seems just as ridiculous to say that anybody who did a sin shouild publically identify themselves as such. No normal person would stand up in a crowd and say "I plowed up a graveyard, and I feel that it is OK, because I observe the rest of the Jewish laws really well." But it seems that Orthodox Jewish Lesbians do just this! If you want to acknowledge the philosophy of Orthodox Judaism, which includes the ideal of living by the laws that Jews have observed for at least the last 2000 years, you cannot be honest with yourself and still say that "just this sin is ok," because you can't always get what you want, and accepting a philosophy is not a piece by piece propostion.

I personally am ashamed if I ever yell at someone, or talk gossip about them, because I acknowledge that it is wrong. I'm not self-hating, or inconsistent because I commit sins, but I'm not marching in a "I'm not so good at keeping commandments" parade.

PS. I would never condemn a person's choices in this regard. There is however, a choice. Gays don't attend Jerry Falwell's services with a pride T-shirt on, and it seems silly for someone to be inconsistant in a matter as important as their religious beliefs.