License for selling software?

[News User]

Hello,

I wrote web application for my wife's lab.  Recently she
showed it to several colleagues at a conference, and now
three different universities want to buy it.  Since this
is the first time I'm selling software, I have two
questions, and my search on the web hasn't shed any
light, so I thought I should ask here.

First,  is it okay to sell the software?  I used BRL
http://sourceforge.net/projects/brl/ which has a GNU GPL
license.  I don't rely heavily on BRL, and it wouldn't
be hard to switch to other library that doesn't have a
GPL license, but I would rather keep the software
unchanged.

Second, where do I find _easy-to-understand_ information
on licenses to check which one to use for the software.  I
want to give them the source code (so they can have an
undergrad make changes if they need), but I wouldn't want
them to be able to redistribute it.

Thanks!

-g.