This is a fairly new game, right?
You may be better to just buy a new card, as even if the game would run you'd probably get very low frame rates from your current card and the game wouldn't be enjoyable.
Try the things Dilbert suggested and see if they fix your problem.
If not, consider a new graphics card.
Do you know if the DXT texture compression...is just a free download or something?
I don't think it would be something you can download. I think it's a feature of the card, and if your card doesn't support it then you can't make it support it.
I'm not really sure though.
I sure am confused, but I have faith in this forum...I really do!
We're all confused . . . lol. You're right to have faith in this forum, we have some really knowledgeable people here.