I just installed a Tuniq Tower 120 Extreme on my Biostar TPower N750a....it's not difficult to install at all, as along as you read the directions. It's also a great cooler. Keeps my Phenom II x4 940 at 35*C Idle, 48*C under full load (4x prime95 + Furmark 1920x1080, MSAAx8, Extreme Burning, Displacement Mapping, Post FX) 43*C with just the Prime95. The hardest part of the install was applying the damned TX-3 thermal paste which, although a pain to work with, seems to cool exceptionally well. (The former statement was oppinion, I have not yet compared it to my old standard, AS5)
EDIT to remove subjectiveness of 'not difficult':
On my board all I had to do was remove the Stock HSF attachment piece, attach the backplate, replace the mounting bracket with the K8/New AM2/AM2+/AM3 mounting bracket, spread TX-3, place HSF on processor, and attach with thumbscrews. It (to me) was not that difficult. Other's may find the extra amount of assembly/disassembly unattractive. In my opinion, however, it was completely worth it.
If you're confident with a screwdriver you should be fine...