Well, I just got through my growing pains with the Dell Deminsion 2400. You probably need to upgrade your graphics board. My Dell had intergrated graphics, so changing that would be a good thing. The sound needs to be changed too. Here is what I went to for these two items.

GeForce NVidia FX5500 PCI 128 (Video Card)
Sound Blaster 24Bit sound card

While your at it, you should up your ram to at least 512MB. RTW uses a lot of Ram.

I would also direct you to check out the post at Dell for the 2400 and all the game sites for upgrade tips. It took me some time to get the hang of switching out components for dell. Oh, by the way I uped my graphics again, but the was a personal thing. The FX should be fine.