There is a few things you could check

first i would stick with direct x 8.0 since u r using win 98se
check in your bios to see if you have the optimal and turbo mode
if you do set it to optimal or it could be normal or power mode
and make sure you assign an irq to your video card so that it is not sharing with your sound card etc
Also if you have windows xp you might want to install it because there is a compatibility option on xp that will allow you to play ur game what you have to do b4 u install the game make sure u go to properties and install with 98 se compatible ,

Hope this helps, I am not an expert just a diy'er