I had a run-in with a pseudo-Bess filter and it seemed (seemed my foot, read * for explanation) that it had a blacklist of web sites it would not allow. URL matches the blacklist strings? Oh well. I'm fairly certain it can do word filtering as well, so suppose you looked for pages about getting around it, it would block pages that it determined contained that information.
Judging from the web site you pointed to, particularly the diagram on the "How it works" page, it would appear that the server with the blacklist is run by Bess. If you can find a way into that server and figure out how to make alterations while escaping the notice of the authorities, I say lots of people would thank you.
Otherwise, you are stuck. It's possible you could get around it with tunneling or proxies, but it's also possible the Bess filter blocks proxy activity.
Keep in mind that taxpayers pay a lot of money for schools to have internet access for the purpose of education, and every bit you download contributes to that cost. If your filter is like the ones I ran into, there are quite a few false positives (allied health always had a tough time researching breast cancer) so it's possible your frustration is real. If, however, you are upset because you can't check your email, read forums, etc., I have a lot less pity. I'm sure if the filter blocks too many sites, one of the school board members will get pissed enough to get the IT department to nix it.
*side story
My school ran Fortres Gran Security which had a "Bess Internet Filter". What this meant was the security app had a blacklist that behaved like the Bess filter, for all I could see. Fortres itself was simple to crack. Stick a bootdisk in, C:>ren FORTRES 0WNED, then reboot. Windows says "Oh noes a dll can't be found" and Fortres is defeated. Later I was able to get the password through social engineering, and it was much easier to use that than to reboot.
The district does seem to run some kind of server-level filter, but it gets confused easily. While working in the Tech department one summer, I found that if you clicked refresh enough times you could visit 99% of blocked pages.
*edit*
Geez, since they are targetting schools, they could have spelled "inappropriate" correctly in their "Sentian Overview" flash.
