This is all based on you using Windows XP as your OS. *IF* you want to play Warhammer at a decent framerate (low-mid settings) on your PC keeping your CPU the only suggestions I have are as follows. Increase your RAM to 2gb (No Exceptions) which is roughly $20 per 1gb stick (No use wasting money past 2gb mark). Your video card will also have to be upgraded. If an AGP interface which I figure you have, then I suggest a Nvidia 7600GS ($85) or an ATI Radeon 3850 ($100). This will make it run at acceptable levels in World RvR and 30v30 Scenarios. Even with these upgrades it's not gonna be a stellar experience, but it will be playable.
I have a friend playing on a AMD Athlon 2400+, 1gb Ram, and Nvidia 6600GT video card. He stays under 15fps on full low settings even in starter areas. A 6600GT is around $50, but isn't a smart purchase decision nowadays imo.

