Yesterday, new jailbreak software has been realease by Geohot. It's greaest new for every iPhone 3GS user.

WARNING :
                      You must jailbreak under WindowsXP 32bit or Windows 7 x86. It will not work under 64bit O/S or Vista
                      RC2 : The jailebreak software is working under XP, Vista, and Windows 7 (32bit, 64bit, and Internation)
                      RC2 : Sign issues were resolved. and now support VM_MEM kernnel fixing.
                      Please make your iPhone (step 2) before jailbreak to avoid some extra troube
                      When restore at DFU mode, remove your simcard to easy unlock.


- 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 :-)


Step 1. dowload purplera1n_rc2.zip   (jailbreak software).

Step 2. prepare you iPhone 3GS as an clean status 
             - Remove your simcard 
             - Restore in DFU mode

Step 3. Activation using iTunes
              - After restore, insert SIM card to activate with iTunes.
             
Step 4. Run purplera1n.exe
             - Just click a button
     
Step 5. Install Cydia
            - Setup WIFI if you needed or possible. It will be faster than 3G
            - You can find "Freeze" in 2nd page 
            - Run "Freeze" and touch "Install Cydia", it will install Cydia
            - Reboot

Step 6. Unlock using ultrasn0w
           - You can unlock using ultrasn0w from Cydia

Good Luck !!!