Why does Modern Warfare 2 Run Better Than Team Fortress 2?

This is to help my brother out.

He never play's team fortress 2 anymore becuase he says it runs too slow on his crappy computer. However Modern Warfare 2 runs fine on it.I saw him play it and it looks good and runs smooth. Graphics and resolution are at a good level and dosn't slow down.Then played Team Fortress and with everything set to low it ran so bad, averaged about 15 fps. Can anyone explain why this might be?

I would have thought that it would have been the other way round as MW2 is newer, and in my opinionwould be alot more graphic hungry than cute ol TF2,but it's not the case.

Using CPU-Z he sent me all the spec on his computer. As I thought this would be either a simple answer, or an obvious hardware problem, I didn't post all the spec. If it's needed let me know and i'll get to work.

Thanks for the help peeps  


Moike