I'm new to square taper cranksets - started out on the current external bearing stuff.

I've got two bikes that I want to replace the cranksets on: a '97 Bianchi Trofeo and an '87 Centurion Ironman. The Bianchi has a 52/39 Miche crankset on it, which works okay but seems to be constructed of case-hardened margarine and looks kinda cheesy to boot. The Ironman has a Biopace crankset in good shape, but it's a 52/42.

I'm thinking about replacing the Ironman's crankset with the Velo Orange compact, and the Trofeo's with either the Velo Orange compact or a used Campy standard. Assuming the BBs are in good shape, do I need to change them to go with the crankset, or is it just an unbolt-the-old-and-attach-the-new operation? If I do need another width, how do I determine what width?

Thanks!