Looks like you have an AGP graphics card... So you need another AGP-type card to replace it.... Unfortunately AGP cards will never be as good as PCI-Express cards because of the AGP limitations, and today its kinda hard to find AGP cards...
You can't use PCI-Express cards, sorry! And even if you change your motherboard, you'll probably need to change the CPU (to socket 775) and RAM (to DDR2) :/
But try to find the AGP version of the "Powercolor ATI HD4670 1GB PCS GDDR3 AGP". You'll find a lot of those for PCI-Express, but it needs to say explicitly that its for AGP.
If you can't find that one then try looking for these:
* Powercolor ATI HD 3650 512MB GDDR2 AGP
* XFX GeForce 6200 512MB DDR2 AGP
* Powercolor ATI X1650Pro 512MB AGP