I know the system requirements of Call of Duty: World At War and my PC falls slightly below them, but only on the GPU aspect. I was wondering was people's experiences were with a PC that is slightly under the requirements. Any input would be much appreciated

If my PC could talk, it would scream its ass off in pain, i always put things on higer quality even tho my pc falls below the requirements.
i think you should get away with it, being the gpu and all,

You may have to lower every thing to the minimal settings but otherwise you should be able to play it.

COD4 was very well optimised and looked quite good too, I don't know about 5 though. Isn't there a demo?

Tried running Age of Conan on the minimum requirements at release and it was unplayable. It all comes down to optimization and often the mininum requirements suggested are still unplayable (same thing happened for Bioshock with me), I really wouldn't suggest ruining the experience attempting to play it like that. If you have a PCI-E slot try to get an 8800GT or Radeon 3850 and you should be fine for mid level gaming.