Q: I keep hearing about there being an untethered jailbreak for iOS 5 if you have the old bootrom on a 3GS.. Any truth to that?
A: Yes…redsn0w will auto-detect that for you and make it untethered if you have one.

This is untethered Jailbreak 5.0 and 5.0.1 for iPhone 3GS with old bootrom. Cool. Untethered Jailbreak 5.0 is cool.

Required Downloads:
Download Redsn0w 0.9.9b8 for:
Redsn0w for Mac
Redsn0w for WINDOWS
Download iOS 5.0 iPhone,iPod, iPad
Download iTunes 10.5 for Windows and Mac

HOW TO JAILBREAK 5.0,5.1 iPHONE 3GS UNTETHERED COMPLETE GUIDE:

1) Open RedSn0w tool and click “Extras”

2) Click “Custom IPSW”

3) Select original iOS 5 and click “Open”

4) Waiting ……

5) OK. Custom IPSW created

6) Click “Pwned DFU”

7) Click “Next” and read information

OK. Your device should now be in owned DFU mode…

9) Connect iPhone 3GS with iTUNES and click “OK”

10) ATTENTION. Click “ALT +Restore” ( Mac OS X) or “CTRL + Restore” ( Windows PC)

11) Select Custom IPSW (file “NO_BB……..” )

12) Click “Restore”

13) Waiting….

14) Waiting…. and Done.

Now you have jailbreaked iPhone 3GS with old bootrom.
If you want unlock this iPhone 3GS with 5.0 read this post: UNLOCK 5.0 IPHONE 3GS / ULTRASN0W