Nawp. Can't be done on a PowerPC Mac (no matter what OS it's running) unfortunately, when I had my G3 iBook I had to use a Windows box to jailbreak my 2nd Gen iPod Touch, & I still have to use my Windows box to this day as a matter of fact.
If you're on Tiger anyway this means you can only run iTunes 9.2.1, which can' be synced with 4.2.1, I believe 4.0 was the last iOS to sync with iTunes 9.