okay well if you dont know if you saved your SHSH, the only way to figure it out really is to try downgrading your 3GS and rejailbreaking. Here is pretty detailed instructions over at
iHackintosh.
if it doesn't work, i would assume you didn't save your SHSH, which means right now you will NOT be able to jailbreak until the dev team or Geohot, or someone comes up with the next jailbreak edition.