at this point, you might should post a DXDIAG ( top 1/3 to 1/2 of it ) here for others to look over, F4U.....
as you said, game runs fine for roughly 20 +/- minutes then suddenly Freezes..... have you noticed if anyone was talking on Vox ( ch5 Vox or F12 local range Vox ), and what type of sound card are you using - dedicated soundcard or board intigrated sound ??? could be you need to also update your sound drivers also......
if you don't mind, please post your computer specs along with the top part of your DXDIAG report...... to let others ( Skuzzy ) see if they notice anything out of the ordinary
hope this helps......
TC