Look around on hotscripts, or google search free help desk software. You will find a lot of free solutions that may meet your needs. A few in .net, some in asp (liberum help desk) and many in php (HelpDeskReloaded.com, OneorZero.com, etc). Look for the ability to easily alter the software, and also what your ability to get support for the software are. Is there a paid support line, or an active forum that you can get help when things go wrong? Also five to ten questions a minute is really high for that user size.

What about the Taelon mothership?