You dont need SHSH on iphone 3Gs, try putting it into recovery mode and then using the tool RecBoot (http://http://bit.ly/cNNCiG) to exit recovery mode, now its going to be difficult and i dont know for sure but its worth a shot putting your Phone into DFU using Last DFU by sergiomcfly.. (http://http://bit.ly/gNiBeZ) that SHOULD get you into DFU, then you should be able to downgrade =P hope this helped
What is SHSH??
I thought it was SSH :?
<Tue Mar 22, 2011 3:19 pm> [hr:1sbiplm0][/hr:1sbiplm0]
Ugh.... I would say try ireb, but no dfu for you 
Maybe search to see how to dfu on windows?
For windows DFU make sure your device is off and pluged in, then hold the power button for 3 seconds, without releasing the power button hold the home button for ten seconds, and keep holding the home button for 30 seconds but release the power button.