uhh ok... the fan on the video card isn't your biggest problem, but here goes. The fan should be held on with 4 screws. Then just pull the electrical connector off the board. Putting a new one on is a different story, get a blue or crystal orb. Problems... the mounting holes might not line up, you'll have to use some thermal epoxy. This is perminent, but the card is already 2yrs old, you got your money out of that card. The wire connection are different, which means you have to do one of a couple things..
1. You could cut the wires on both fans(they will be the same color) and wire the 2 wires together(using solder, or self sealing butt connectors)
2. If the pins are the same size theres sometimes a way to pull the pins out of the connector, then reinsert in the old connector
As for risk, just the risk of esd damage to the video card, not hard to do.
As for the blue screening, what were you doing leading up to the event? It's unlikly that this fan problem is the cause of that blue screen. My guess is that you have 1 or 2 problems, 1 that HD you have doesn't seem good, errors shouldn't be happening. I'd scan disk it every couple days if theres errors popping up then its toast, buy a new harddrive give that one to the leech that askes for free computer parts all the time.
Get a program that will do a stress test on ram, usually when it does the mem dump thing its a ram problem. I could be wrong but it won't cost you anthing to find out.: