No, not drop the processor speed but reduce the total amount of video memory used. Some 3D video programs have problems not only with too little memory but sometimes with too much video memory.
So, I thought you might try to reduce the amount of memory allocated to your video processor. This is usually done in the BIOS at boot up time by entering setup mode. My hunch is that over 1 Gig of video memory is too much.
So try setting it to 512Mb or less and see if it helps. If it does help, work your way up to higher numbers until it stops working.
-- ggunners