7900pcie or 7800agp

ok heres the deal..i would love to get the new 7900, but i only have a agp slot...i was thinking about buying a pcie mobo to get this card, but i have socket 478.and socket 478 pcie are almost impossible to find..but i found one

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=6855798264&category=44943#ebayphotohosting

do you think it is worth it to spend an extra $100 dollars or so to buy this card or should i just stick with the 7800gs..also, would this mobo itself be a downgrade from my current ic7?-thanks

This is a somewhat tough question to answer.
I'd probably be going for the PCI-Express card, because when it later came the time to upgrade cpu/motherboard & ram, I wouldn't need a new GPU at once. If you go with the AGP card, you will have to change your entire rig in the next cycle, but if you go for the PEG (PCI-Express Graphics) card, that wouldn't be the case.

Of course, you might want to ditch your entire rig later on for all I know, but if you prefer to make small upgrades, that's my recommendation.
But looking at a review, it seems it shouldn't be a downgrade, but could actually be an upgrade.