Just to add to what Jack mentioned. You can run more than two PC's in ad hoc. You just wouldn't be associating through a central device. PC1 would talk with PC2, or PC1 would talk to PC3, or PC2 would talk to PC3. No central access point, a wireless peer to peer network.
Also, you can setup a client device as an AP with Linux. I am a bit suprised there isn't a window equivalent by now. Never tried it and I agree with Jack again (WTF), go buy yourself a 30 router/AP combo and be done with it, unless you just like trying stuff, have a box around to throw linux on and are relatively proficient at the OS.