A P4 3.0 ain't bad, but it can't keep up with the AMDs as far as gaming and everyday usage goes. The P4's shine when it comes to video encoding and such.
$300? Why? You can get a 3000+ for $147, a 3500+ for $201, a 3800+ for $282. But if you want to spend the money, you can get a 4000+ for $334, a X2 4400+ for $497, and a FX-57 for $1011.
The FX-57 runs at only 2.8GHz, but there ain't a P4 that can keep up without major overclocking.
so what exactly makes a video card good?
The GPU of the card can make or break a vid card. Be sure to not only look at how current the GPU is, but at what speed it runs at, as well as the speed the RAM runs at, what type of RAM it uses, and lastly how much RAM it has.