@Nabs: About GNU and GPL.
GNU is a project that promotes the idea of
free software, an idea which was the major inspiration for
Open Source which came years later.
GPL is a legal document written by the people behind GNU (the
Free Software Foundation). It's a software license that implements the ideas of free software as well. Mainly that users should be free to modify and distribute software as they please.
You can do business using open source/free software without any problem. Commercial licenses are something different. GPL has one main restriction: as a programmer, if you modify the code you have to publish your modifications under the GPL as well. Some commercial software companies don't want that. (For instance if you want to include TightVNC in your product but don't want to make your product open source), this is where the commercial licenses come in.
If what you want to do is use TightVNC without modifications and sell support on top of it, you're 100% free to do so. From
this page (emphasis mine):
TightVNC is available under the terms of the GNU General Public License (usually referred to as GPL). This is the primary type of licensing, you do not have to pay for it or enter into any special agreement. Just download the software and use it for any legally allowed purposes, including commercial use.