I have a desktop with an intel p4 2.53 cpu (not my primary pc). The mobo only has PCI and an AGP slot. I've read that a fast gpu with a slow cpu and vice versa is bad. So will this card : Radeon HD 4650 agp 1GB DDR2 run okay on that desktop or should I just get something like a GeForce 6200 AGP 512MB DDR2. Keep in mind I only need a gpu that will run something like TF2 okay, but if that gpu or the cpu is too bad for that, let me know. Thanks in advance.
I think that those will run okay together. Even if not, it is not "bad", it just means you are not getting full performance out of one, but the other has all of its power being squeezed from it. Go ahead and get the ATi, You should be fine. Also, If you are worried a lot, look into OCing.
The idea of balancing your system isn't so much about bad and good, but more about being wasteful.
To know if your CPU is good enough, you'll want to just test out games set at their lowest settings. If they are still unplayable now, it probably wouldn't matter what GPU you put in it, the CPU just can't function well enough for gaming.
Picking the right GPU is generally best determined by what resolution you play at, but also the games your CPU can handle. If the CPU can't handle modern games, then you need to judge the GPU requirements on the games the CPU can handle at the resolution you are playing at.