you dont need a mac, in fact, the money you save on not buying a mac will allow you to buy more plugins, synths and hardware etc for your production.
I have a desktop running 64bit win7 with 8gb RAM, cant remember CPU speed off top of my head, but that runs everything I have perfectly, and I dont work light! I have an automated DAW controller/mixer, Cubase 6, Kontact, numerous plug ins and VST intruments, around 10-15 tracks of audio per project and my pc has never struggled with that. Dont be drawn into the whole Macs rule for music production, yes they are good but you dont need it, save your money and get some decent mics and software!!!