sure.. the best agp gfx card you can get imo is a geforce 7800gs but if you just want to play runescape then you might as well get something like:
radeon x1650pro AGP (about £30-40)
or radeon x1950 AGP (about £50-100)
they go for even cheaper on eBay but make sure that the card is AGP model not PCIe

as for ram as I said if you want to use XP then at least 512MB and for vista at least 1GB
look for ram that says DDR400

Right OK can I play the latest games like Call of duty 4 or not?

These are the specs for it -

Intel Pentium 4 2.4 GHz or AMD Athlon 64 2800+ processor or any 1.8Ghz Dual Core Processor or better supported
512MB RAM (768MB for Windows Vista)
8GB of free hard drive space
NVIDIA Geforce 6600 or better or ATI Radeon 9800Pro or better

if you plan on playing cod4 then definitely go with at least 1GB ram and a radeon x1950xt or if you have the money the 7800gs... I don't know how AGP models perform with latest games but it's the best you'll get without getting a new mobo

I highly doubt you'll be able to max out the settings though

Man I'm sorry, but I'm just so confused lol. Do you think its worth putting money into this MOBO then? Or do you think it's a bad idea? Thanks for all your help.

Nah don't bother putting big money into it as its about 5 years old

What so buy a new one?