Geohot recently updated his program to jailbreak the iPhone 3GS (purplera1n) so that it is now vista compatible.
Improvements:
- Vista, Windows 7, International, 64-bit support
- Less flakiness in the payload
- Cydia tar cleaned up
- Improved logging with slightly more useful errors
- New kernel patches, codesign errors gone. Props posixninja
- Added vm_map +x, passed vm_check
- No winterboard yet, but now that ball is in Saurik’s court 
You can download Purplera1n for iPhone 3gs here: Purplera1n (UPDATED) (0)
Steps.
1.download the program save it in your desktop.
2.update iphone 3gs to firmware 3.0 ( this won’t work on 3.1 at the moment )
3.just launch the program.
4.after it do the trick.
5.you’ll see an icon in your iphone springboard that says FREEZE
6.click on it.
7.and then click install cydia.
8. DONE.
For Unlocking it.
1.Open Cydia add the source ( http://repo666.ultrasn0w.com/ )
2.it will load then after that look for the package called Ultrasn0w.
3.install then reboot.
4.then your ready to go!
oh yeah for T Mobile users you guys need to turn off 3G 1st before using the Ultrasn0w.
Credits : Dev-Team , Geohot. thanks GUYS! 
