Windows 7: Quick Questions / Easy help asked

Okay, my situation:

What I am asking: I am looking to upgrade or get windows 7. Will I run into any problems? What Windows 7 should I get? Is it worth it?

500GB of memory
6 GB ram
corsair 750 watt power supply
Currently running windows vista 64 pit premium
Now I got a nice ATI Radeon 4870 x2 graphics card but it has had some serious problems ever since I got this computer.

First - I got this computer from cyberpower, nice place and all, like 2 years ago, they didnt send me the vista 64bit premium disc with it.. so i dont have something to fall back on. So the reason I bring up this issue of the graphics card is because I feel installing a fresh windows 7 on the computer will possibly corrupt the ati radeon graphics card that was never properly working. I dont know much beyond it hasnt worked properly for me.

-I also have a laptop I would like to apply windows 7 to. And I do ike to reformat my comps when I run into issues - so having an unlimited windows 7 supply may be needed. so my questions

1) Should I buy the three upgrades windows 7 in hopes that I dont have to reformat ?
2) Or should I buy windows 7 premium full? I am currently leaning towads this - as I love to be able to reformat etc.
3) Does wndows 7 completely reformat the comp / everything on it?
Will I have to install the drivers again - especially the ATI radeon driver that always has giving me problems.

Thanks for any help here mates.

You can do a format with the much cheaper upgrade.
Clean Install with a Upgrade Windows 7 Version[2]=General Tips
trust me on this if you qualify for the upagrade. The upgrade is the same as the full value, excpet it costs a lot less.