dude a 7600gs will be no better than your x 1600, they're the same, basically.
yes the 7900gs will be better. and no, i have it, it does not have 2 gpus. but the one it has is a monster. and if you have a 6 series gs equivalent card (sic x 1600 or 7600) the 7900 series has some advantages that will be worth an upgrade.
unless u want to wait for 8800 (driver problems) or x1900 xtx (overpriced).
"nagasama no longer drinks tecate, or streaks out of the night for anything, and he has a fine wife so he has no use for your girlfriend...she is safe..."