... what your current PSU is. Your choice of PSU also depends on what other hardware devices are running in your PC, e.g. top end graphics cards are power eaters!
click here will help you decide whether your current PSU is up to par.
If your case is ATX there should be no problems.
The only way I know of checking your P4 is plugging it into another mobo and seeing if it works!
Hope this helps!