don't ask for details as the following steps all have tutorials written for it already.
reboot your computer after installing itunes 7.5 or older
get your iphone to restore mode, then use ibrikr to enter DFU
RESTORE to 1.1.2, it will fail
restart computer, restart iphone, enter DFU
restore 1.1.2 again. this time it should work, might give you some error
use ibrikr to kick it out of restore, if it worked and your iphone rebooted, congrats. do your thing now.
thanks imm .. trying it now