I you have an
Ipod Touch 2g mb
Iphone 3GS old bootroom
or Iphone 3G
Yes you can and it's simple get redsn0w.
If you have a different model for example 2g/3g 8 mc model you need to down grade to 3.1.2 then use iH8snow' Sn0wbreeze 1.7 to jailbreak.
If you have an iphone 3gs new bootroom or Ipod touch 3g 16GB 32GB you need to have backed up SHSH blobs. then Use iH8snow' Sn0wbreeze 1.7 to jailbreak