Is it possible to tether with a jailbroken 3gs that has OS4? If so is there a how to, I have searched quiet a bit and found no definitive answer

I believe there are tethering hacks for non-official carriers, but due to how the carrier settings are applied (signed, now), if you're on an official carrier, there is not a tethering solution short of replacing the commcenter with one from an older firmware. There's a forum post about this here:

http://www.hackint0sh.org/f236/121326.htm