Mysterious OpenGL lag

[HeX_Vulture]

(I'm posting this here since I can't get a good answer on the ST forums)

OK, my brother's computer has a graphics card that can run great on _most_ maps.

However, Greenwar map20, KDiZD z1m3, and every single one of Mechadon's maps (no Sabbat Martyr for me in GL) lags it to crap. It works fine on software however.

The graphics card is a GeForce Nvidia 6600 VE 512MB GDDR2 PCI Express DVI/ VGA

The computer specs are:
Intel Pentium D 833 3.0 GHz, 2MB Cache, 800FSB, socket 775
1024MB PC4200 DDR2 533 MHz memory
Using Windows XP Pro with SP2

Anyone know why the crap a vanilla map lags? He overclocked it once and it jumped up the main processor usage to 99%, and in the end it still lagged. I recently updated the drivers and it didn't help.

http://www.skulltag.com/forum/viewtopic.php?f=3&t=9542