The SDK is only available on OS X, forcing you to use a mac. If you don't want to purchase a mac you can either run OS X on a virtual machine on your windows box, or you can install OS X on your PC.
In my experience the virtual machine solution is unusably slow (on a core2 duo laptop with 2G ram). If you feel like trying it search for the torrent. It's probably not worthwhile.
The other option is to install OS X on your PC, commonly referred to as a hackintosh. Hackintoshes work quite well - my friend just sold his mac because his Dell quad core hackintosh was actually much faster than the apple hardware (and cost about 1/3).
Of course both of these options are likely counter to some licensing scheme, so proceed at your own risk.