I grabbed a copy of the GPL'd bandwidth arbitrator software today.. just to see what it was all about. In a nutshell, they provide a patch for the 2.6.5 linux kernel bridge code (their entire system relies on bridging to deal with packets between interfaces).. the rest is a set of perl scripts.
The biggest differences from their commercial offering compared to the free version (aside from the hardware itself) is a couple of nice things like a web front end and some rrd graphs.. the configuration is very well documented and in reality should be actually fairly trivial to setup and get going.
If you'd really like to have your own netequalizer-like system then my advice would be to save yourself a bunch of cash and roll-your-own.. if you and/or your staff aren't up to the task then you can still save a big fistfull by setting up a very basic linux box with a build enviroment and grabbing a 'coder for hire', for a less than a thousand bucks the coder-for-hire guy(s) could do a 2.6.5 kernel build and make a web front-end tailored to your needs rather than you and your staff having to learn what's provided.
Just my 0.02
Why don't we just take the safety labels off everything and see what happens?