Is it reasonable to replace 7900GTX with 9800GT?
I have a ATX PSU 480W Delta Electronics DPS-460DB.
Will it run 9800 GT without problems? Or do I need to get a 500w PSU?
The 9800GT needs a 450W PSU with 26A on the 12V rails, so if you got at least 26A on the +12V column(s) on your PSU, you will be fine.
The 9800GT is placed 5 tiers above the 7900GTX in the GPU performance table so it is much better (a good GPU upgrade is at least 3 tiers higher).
You should be all fine. your power supply will be enough.
I would strongly suggest going with a more current card. Something like a GeForce 640 or a 650. Those should be on par when it comes to performance with the 9800GT. In real world use the 600's will consume far less power, with more current drivers it should perform better with less sluttering. In the long run it will make your power supply live longer because the 9800 is quite power hungry.
He posted his computers model and number. It's a HP d4595. That computer is using a Athlon 64 X2 (W) 5000+ 2.6 GHz processor. Anything from the 600 series would be severely held back by the processor, and that's if the graphics card manages to fit in that small case.
the 640 and 650 are tiny cards, some providers actually make a desecrate model for the 640 and the 650 is probably no more than the size of the 9800gt. So i believe your comment just collapsed on itself...the case is more than big enough for it. Also the chip won't bottleneck because the card doesn't perform that high. PCI-E dsnt have a drastic performance difference from x8 to x16 and PCI-E 1.0 vs 2.0 isn't that drastic either. It may not perform at max, but the 9800gt doesn't perform like the big graphics cards today. So the performance loss is VERY minimal...the card should be VERY close even when it runs at PCI-E 1.0 x8.