I own a Zalman (after my stock fan crapped out and my proc nearly leaked out my vents . . . I saved the proc and stuff tho . . . (holy sh*t! 90 deg celsius! RUN!!!))
its easy to install, but a little wierd. The clip goes on easier than a stock amd hsf, but the fan is seperate, and you screw it onto your PCI slots (you know, the one screw you need to hold stuff, you just put it on top of the PCI card's metal back thingy and put the screw through both of them) . . and the fan is a 92 millimeter, so you sdjust it so its over your hsf and it also blows on your mobo or ram, depending on where you put it. Its easy to install, but it takes a bit longer. works better than stock, also.