Bank 1 on your 3800 Series II Engine would be the set of cylinders that is closer to the front bumper of the vehicle (cylinders 1, 3, 5). Bank 2 (cylinders 2, 4, 6) would be against the firewall.
The Leak... Any vacuum-leak hunt shouldn't start without having a clear vacuum-hose diagram in-hand. There should be one on a placard inside the engine bay (possibly in the radiator mount area or the underside of the hood). Here's what it looks like.
If the vehicle does NOT have a supercharger then the vacuum system should look like this:
If the vehicle was equipted with a super charger then it should resemble the following:
Use this map to trace every vacuum line. Even if you cannot see the mall you should be able to feel them from start to finish to make sure they are connected at each end and do not feel fray'd or brittle or damaged in any way. When vacuum lines become "old" you can twist them in your hands and they'll being to break apart. You could also bend/kink them and they'll show cracks and signs of dryness. This means it's time to replace them. Remember that a lot of small leaks will have the same effect as a large leak.
The cigar trick actually works since a cigar has a very thick smoke. Also a fireextinguisher would work, but could get rather messy if you mess it up. You could also check differnet areas with a vacuum pump and pinch off areas to test sections at a time. But this could also get a bit trcky if you're not familiar with the system and don't know what you should be pinching off at what times. Either way any of the "quick" methods stated are all very "hackish" and nothing to be considered as "good practice"..
The vacuum leak is one of those issues that no mechanic loves to diagnose. It's usually either diagnoses in 10 seconds or it turns into quite the migraine. I'm sure that most mechanics would have to agree with me that in order to properlly diagnose an issue like this it must be done correctly and without any short cuts.
I've always attacked issues like these with a smoke tester. I have 3 of them personally. Even if the leak is obvious I will still smoke the vacuum system before and after the repair to ensure that there are no other obvious leaks. This will ensure that the vehicles doesn't come back with the same issue & the same cause. If the vehicle was to return without any leaks then it's time to look at one way check valves and switch-over valves that would cause internal leaks in the system. But, that's a whole other story.
So, check the hoses thoroughly, and if everything checks out. Then it's time to bring it to a reputable shop.
Hope this helps.