You will need a new PCI-e compatible motherboard as your socket 754 motherboard doesn't support it. And depending on your choices, you might need new RAM, although that's not necessary. You can tell us your RAM speed by downloading CPU-Z
Alright, so what is your budget to work with? If you have a really low budget, you might want to go for a cheap AMD motherboard. If you prefer to hang on to your cpu and memory for a bit (although the memory can't be upgraded then) get something like an ASRock K8NF6G-VSTA
However, I would only suggest this if you're on a real tight budget and want to upgrade as little as possible. If you've got some room to work with then it's best to buy an Intel Core 2 Duo E6300
with a nice Gigabyte 965P-DS3
or an Asus P5B-E
motherboard. However, anyone can tell you this information, so it would be plentily available if you used the search.
I'll give you this advice whatever you do: If you want to upgrade to a DX10 video card, you will want a very fast processor to get the most out of it (an Intel Core 2 Duo with suitable motherboard) and that also means you will
have to upgrade your memory to DDR2. And I can't imagine that, if you're willing to splash the cash on a videocard, you're on a very tight budget for the other components.