If you screw the fan on, the shop might not want to take it back if you have to make a warranty claim. A cooling modification like that is a strong suggestion that you've overclocked, even if you swear you haven't they might not believe you.
I had a spare socket 7 fan and there were 2 holes in the PCB that line up with the mounting holes on the fan. I tied it on with fishing line, the card is cool and there are no permanent marks. Alternatively you could try the trick of bending an expansion slot cover around and bolting a fan onto the slot cover, then screwing it to the case. But I went the fishing line option cos it was easier
Just gotta check it every once in a while, fishing line can stretch over time. Wondering if there are any plastic spacers or something so i can attach it to the board directly and have a solid mount.
Kinda sidetracked there, yes I would go and buy a fan if I was you. I could not hold my hand comfortably on the viper 550's heatsink when it was running, in my opinion that is too hot. My friend reported smelling hot PCB coming from his computer, obviously because of his Creative Labs TNT card. Not burning, just a distinct odour.
Cooling can't hurt, and it's fun setting up a good, cool system. Go for it.