wow...where to begin...
It is possible technically to use a joystick as a mouse, however it usually sucks. a trackball is a much better option.
i believe most wired xbox 360 controllers will work with windows xp sp1 and higher simply by plugging them into a usb port.
as for computer specs to run mame, that depends on what games you want to be able to play. some games only run on 4ghz overclocked core 2 duos, most will run on alot less. It also depends alot on which version of mame you are using. i have a pentium III, 800mhz with 128mb of ram, running win98 that will play most of the vertical classics with no problems, using an old version of mame.
as for my main cabinet, i'm running a p4 3.0ghz, 2gb ram, geforce 4 mx440 graphics, and it runs most games just fine (3d games don't do so well)
my suggestion is look through the wiki, and try to get an idea of what you want to accomplish.