Will be more intensive than wow, thiking around bf2142 level gfx

Remember that you will optimally want a large viewable distance and dozens or even hundreds of ppl can be onscreen at one during a siege....

If you can, id upgrade to a ATI 4850 or better, or Nvidia 8800GT class or better and have a phenom 9000+ or core2 6600
or better.

Which is really cheap to put together nowm, relatively speaking.