books explaining laws

[ged25]

Are there any good books that explain the legalities involved in selling proprietary software or running a web service etc ?

Also is it legal to make a proprietary closed source application using a GPL software ?
As I understand it, you only need to release source code if you modify the GPL software itself.
Am I right ?

[WingedPanther]

I don't know about books, but GPL software can get VERY tricky. Some have a linking exception, others don't. It depends on which library you are using, and how you are linking to it.