Help me with DirectX please!!!!!!

Aggggrg - please help! I have a PentiumII running at 333MHz, 128MB RAM and 8MB ATI Rage Pro Graphics Card, with Win98. I have the latest graphics driver from ATI which is fully certified by my working copy of DirectX6.1. Even then, I cant get any games that require directx to run, incl. Quake II, Simcity 3000, and Janes IAF. All that happens is the game runs perfectly for a minute or two then either crashes back to desktop or the PC freezes.

I have tried everything, all the troubleshooters (grahics acceleration slider bar, different resolutions, closing down applications in the Taskbar, the LOT! But nothing works, not even the game web sites or the ATI website can help.

Is there anyone that has a similar problem or can help me solve this please?????