I've talked to a few people about adding a supercharger to my 2001 Bonneville SE. Many agree that it can be done but I'm interested in what parts would I need and/or if it is even possible.

Yes, it can be done, but it'* going to be a bit of work.

You will need.
L67 heads
L67 LIM
Supercharger
Fuel rails
Injectors
BCS kit for wiring harness.
L67 Harmonic balancer
L67 ICM bracket
L67 tensioner
#9 idler bracket
belt
And last but far from least, a good tune.

Thanks for the quick reply! So would it be easier/cheaper just to swap for a supercharged 3800 or go for swapping all the parts?

That will depend. Your looking at about $500 in parts, about $200 in gaskets, plus the tune. You may also need to upgrade your transmission if you have a 4t65e. Upgrading that to a 4t65e-hd is easy, just change the output shaft, diff, and diff cover. Perhaps $100. The tune will be the problem. If you have your own software, $500 you can do it yourself, but the learning curve is a bit steep.

If you can find a good L67 engine, you will need to also get the wiring harness and PCM. Swap that all out and your set.

do a search for my post on bonnpro performance section. walks you thru whole thing. i suggest at least starting with stock throttle body and maf. doing so makes tuning SOOOOOO much easier when trying to tune it and get it running!! then if you want to add that stuff it a lil easier. i had hptuners...and i stil spent right at a grand. but i did some extras cause that what i do lol