Heya Zelda,
Technically games will look better in Vista if you have a DirectX 10 capable video card...which you don't. DirectX 10 has some nice new features and when games are written for it, it looks dang nice.
If you are going to run Vista, I would recommend a pretty beefy PC if you are using it just for games. Vista is a performance hog by itself, let alone when you are running video games on it. I keep XP on my gaming machine just cause I get a better framerate performance out of my games....which is better for headshots

It's not an incredible deal to me if the game has a few cooler effects in it. But that's just my opinion obviously...
If you have a 7300GT, I'm guessing you have a mid range computer. Upgrading it to Vista is just going to degrade your gaming performance even more. My recommendation may be different depending on the specs of your PC. Let me know what you have and maybe I can throw some advice your way if you want to gear up for Vista.
