Maybe you should read the dev teams official line on thier blog about Windows:
The Windows version needs further testing, so for now this is available only for Mac OS X x86. The Windows version will come as soon as the bugs are ironed out.
For 3GS, to use custom firmware (from pwnagetool or snowbreeze), the phone needs to be already pwned JB. Last pwned JB was Redsnow 3.1.2 or Spirit 3.1.3 + Spirit2pwn (Cydia).