locking a user into one directory

[Dragoncrest]

	I've seen this explained before, but I've never taken much interest in it 
as I never had a need for it.  Well, it's starting to look like I do.  What 
I'm wanting to do is give shell access to a user to shell into the mail 
server, check their mail, and that's it.  I don't want them to be able to 
wander outside of their home directory.  I think it's called a jail, but I 
don't remember.  Does anyone know what it is I need and have a tutorial for 
it or know where I can find one?  Much appreciated.