Buying a minimac just to edit video is probably not the best idea (and I will be stoned to death by the Mac lovers).
I use both Mac and PC, they both have their pluses and minuses. If you have a good PC, keep it, and get decent editing software (Premiere Pro does well). You really don't need a Mac, nor Final Cut. Most people I know with Final Cut can't use it past the features that any other decent editing software has, for any platform.
If you need a postFX app as well, AfterFX, Combustion, are good choices.
Premiere Pro will do all you need from editing to transitions, titling, audio, color correction and simple FX and bluescreening.