Gentlemen, I present to you the civilized social and completely non-liberal-arts discourse of a married man. Rollo tested, kid approved!
Seriously, maybe it's not the best advice for a brand new poster to gamble $750+ of his money on what amounts to betting he'll remember to sell before G71 is announced. IMO,
1) if you want to buy now (not many of us want to live 5 weeks without a gaming PC) and don't want to upgrade soon, get a ~$500 X1900XT;
2) if you want to buy now but still want a 7900 when it's released in a month or two, you could probably still go with a X1900XT and not lose much money reselling, but you probably stand to risk and lose less by just getting a ~$300 7800GT and selling it for a 7900;
3) otherwise, if you can wait, then wait. There's always a better card or a better deal coming down the pipe. The only question is when you decide to jump in. 5 weeks isn't that far away if you have a half-decent card to ride until then, and it's very unlikely that X1900 prices will rise in the meantime--so, worst case, you wasted some time waiting on a X1900, but you'll pay a bit less.
Let's not get into whose marketing is dirtier, as they've both proven lamentably capable in that regard. I think a 7900, whether it be a hugely OCed 7800 or a 32-pipe at "just" 550MHz, will be quite capable of competing with and possibly outperforming a X1900 (heck, Hexus' supposed 7900 GTX 3DM06 score is nothing to sneeze at, tho we have no way of verifying it). But it's a question of waiting for possibly faster card at a possibly equal price, or just taking the plunge now. As long as you know that any PC component you buy will drop value as fast as a "new" car (car analogy = thread OVAH ), then you're good.