Buy an Xbox 360 controller for PC, problem solved. Or if you have xbox controllers already, cut and splice some wires into a Male USB cable (they're the same color so its really quite easy, yellow wire gets taped up and not spliced into anything).
The big hulkin old school Xbox controller (not the s-type) works great for N64 games (6 face buttons, all nearly where you need them for the correct layout. If only the white and black where larger and a bit to the left. But you get used to it).
I used to use a Radio Shack USB adapter, and still plug it in for SNES and PSX emulation. But for games on my PC and n64 emulation...it's xbox duke or s type all the way. The radio shack one worked fine, just needed tighter analog sticks which the PSX and PS2 sticks were deifnitley not as tight as the xbox ones. I still got my radio shack disk sittin right here, so if you wanna chance some different drivers with your USB adapter (not sure if it would work or not) I got em. They were pretty keen drivers too. But I wish more drivers were like the xbox ones (where you can assign any button to any function any controller could possibly have actually making use of the analog buttons on the ps2 controller would be nice).