Even though I am usually the last one to jump on the "don't re-invent the wheel" bandwagon, I feel that mikfire is correct - a good bug reporting system can get very complex very fast. At the very least, modify one of the existing ones heavily to your particular uses. A nice one to use is bugzilla:

• http://www.mozilla.org/bugs/source.html

(it's number one in the list referenced above) It's almost free (uses the MPL, an ugly cousin of the GPL) and definitely has had lots of real-world testing. I also highly recommend GNATS, which is GPLed.