I have run GW on an AMD 1500, 256 ram and 32 MB onboard shared video. It ran not as bad as i expected it too. It was actually quite playable. A little laggy when in heavy battles but was still playable. This would have been about 9 months ago though and i'm not sure how Factions would run on it.
Have you made sure the video options in the game are turned right down? You should try this if you haven't already and if it runs better just gradually turn the options up until you find a happy balance between playability and visuals.
Also try the -image in your GW shortcut to uncompress all the files before playing. It will take a while but saves you alot of waiting in game.
If you don't think you can put a video card in without needing to replace the motherboard then i doubt the new ram will be much better. If the motherboard will take new ram however it won't be a loss even if you have to replace the PC as you will already have new ram