I didn't make it!
I could get a HP Pavilion a1730n on a pretty good deal for about $600
it has an AMD 4600+ 2gb ram 320gb hd dvd burner
Asus motherboard A8M2N-LA
with an onboard gpu
but also a PCI-E slot.
Which power supply can i get to fit in this? Or should I strip all this and put in into my Antec p160
if I want to run a 8800gtx
If you've got a p160, I'd put it in that. It'll be better than any of the junk that HP ships their computers in. If there's anything in the p160 you could probably put it in the HP case with no trouble.
Why not just buy the parts with the $600?
HP use propriatory junk. You'd be better of buying the hardware and building your own. Don't be tempted by the cheap tag.
$60 odd dollars over budget but still a much better build and peace of mind from your own hardware/build, not HP.
Your choice, I'm just helping you get more bang for your buck.
My HP does not use a proprietary mobo or PSU. I would buy the computer, and upgrade the PSU, and stick a new video card in it.