Normally, regular screwdrivers are all that is needed, unless you are disassembling something where the screws seem way to tight, in which case I will occasionally resort to using a very small cordless driver with whatever bits & extensions are needed to reach the screws....
I do NOT recommend any type of power tool for assembly, as it is way to easy to strip the screw heads, which would present a real problem for disassembly, or even worse, over-tightening the screws and cracking/breaking something in the process, which might end up as a very expensive, hard-learned lesson, considering how much good mobo's & GPU's cost nowadayz