I currently have a 3g that is JB & UL on 3.1.2 and works great. I picked up a used 3gs running on the old bootrom and 3.1.3 My question is how can I activate and JB & UL without a itunes update. I dont want to jeopardize my current 3g. Can I update itunes to 9.1?

1. Update itunes to 9.1 ( 3gs is in emergency and connect to itunes mode)
2. Jailbreak with Spirit
3. Unlock with Ultrasnow

Don't need this iphone right away should I just wait for the iso 4.0 JB & UL. Any advice you guys can give me would be great.