Our school has just installed Igear, and it is truly stupid. Check out peacefire.org - it has a section on Igear which lists reasons why it is not good. For example, someone managed to decrypt part of the Igear blocked sites list and test the URLs contained within. It turned out that Igear has a SEVENTY SIX PERCENT FALSE POSITIVE RATE! Of course, if you are currently behind an Igear firewall then, predictably, you can't: the site is listed in all of Igear's blocked site lists - egames, shopping, crime, hate, gambling, news, sex/* and so on.
Anyway, some practical advice: Since it's installed on your network's gateway, there's not much you can do about bypassing Igear unless you have access to the server it's installed on. If you can find an Anonymizer clone that isn't on Igear's list then you can surf unrestricted - until it is discovered by your IT department and added to the list.
Technically, if you have access to an authoritative nameserver then you could add a record pointing to the IP address of the site you want to visit, and then specify the IP only in your web browser; Igear would then look the IP address up and find your bogus hostname, which of course won't be on their lists. This not a practical solution.
Finally, if Igear refuses to download files because of a "blocked file extension" then all you have to do is append a question mark and a random string to the end of the filename. For example, to download HOT-PRON.mpg just request "http://server.com/HOT-PRON.mpg?igearisapieceofshite" and Igear will let you. Why? Because Symantec's programmers obviously have no idea how the World Wide Web actually associates files with their appropriate types.
UPDATE: My school appears to have upgraded the software so that the querystring trick with the question mark no longer works. We got around it by creating a simple proxy on a friend's Win2k system, and requesting <http://likeidtellyoutheaddress.com/pa.asp?http://somesite.com/hotpron.mpg?somesecurityhuh>.
We also installed ngrep on a machine in a computer room. The results were most illuminating: our school uses repeaters rather than switches. Not particularly interesting, until you realise that to log into Igear you have to enter your domain username and password which are transmitted to the server in plain text. We ran ngrep in the background, listening to all traffic for i_server:8002, piping its results through grep and into a large text file. The result was two lovely columns of usernames and passwords.