Ive just overclocked my new ati 4850, lucky for me ATI drivers actually have a part where you can pretty safly overclock them their. But for that card you should get riva tuner, it can overclock pretty much all nividia cards and is the most popular program to use, and very safe as you can moniter all sorts of things with it like heat and fan speeds, also its alot safer then doing it the old fasioned way of bios
, you should just type in "overclocking (you gfx card name)" in google thats what i did, and found a way to speed up my fan speed
thats anouther thing, dont overclock unless you speed up you gfx card fan, or even better getin anouther fan. but for now i just made myine a little faster without it geting to noisy and got about 20% performace increase out of the card which was pretty good.
and yeah it is possible it could set on fire, but only if you make it flamable. all gfx cards these days are made to be able to overclock by manufactures, so that shops can make premium models for them. so you can infact buy cheap study up and get £100 increase in performace
good look, tell us how it goes.