Bought a set of 2003 service manuals for the Vette
on Ebay for around a hundred bucks. They came in
2 days. 4 telephone book sized documents. So far they
look very good. If you want take a look the guy has
2001 and 2002 also. They look exactly like the GM
issued books. Was going to spring for the Helm books
but they were about 200 bucks and not sure if they
had this much detail.
I originally picked up CD versions of manuals but wouldn't recommend them. They are not nearly as complete as the hardcopy manuals. The CD's I have don't show the details for each model but try to cover all GM models from the 1980's to Current year. There may be other CD versions available for a specific vehicle that are more detailed but I don't have any experience with them. The set I have you can also get on Ebay for around 30 bucks but I would say don't waste your money. They require you run an application called Apache under dos which can cause problems with some of the Windows OS's.