Thank you guys, Finally after 6 hours for rigurous following through the document. I finally downgraded , untethered jailboroke and unlocked my iphone 3gs which was running 4.3.4 which supports only tethered jailbroke. 
Here are the steps i followed in brief
I followed through the link
http://forums.macrumors.com/showthread.php?t=1211718