I'll try and disect your questions,
The issue here is that you need to add the IP address and/or the FQDN of the smotthwall box to the proxy bypass in IE. What is haapening is that the bypass page is being proxy'd and filtering itself and kind of getting caught in a loop :)
Also, if a page is blocked, and I try to allow the site for 30 minutes, I get to the SW login where I enter the admin username and password. After I submit my admin logon credentials, I then get a 400 error page that says "This error (HTTP 400 Bad Request) means that Internet Explorer was able to connect to the web server, but the webpage could not be found because of a problem with the address."
Sounds to me like its file security on http for the group that is accessing GMail. I would try the following:
But we get a username/password prompt when we try to attach a file to a gmail message. The IP address is that of the Smoothwall server, but no matter what username and password we use, we can't get through. The browser locks up. If we cancel the logon prompt, the attachment simply fails, but the browser doesn't lock up. What is weird is if we log into gmail with https, we have no problems....I guess because we have https intercept turned off. There obviously are workarounds (tell SW to not authenticate/cache on visits to gmail.com or have gmail force https), but I really don't like workarounds.
1 - If GMail is an allowed site see if adding a permanent bypass for the required group will work.
2 - If you don't want to do this have a look at the smoothwall file security policy to see if that is blocking you.
Yes and no, IE is quirky and can present problems but most of these can be worked around and I am sure that scores of others that use this product on here (like me) will be able to tell you the same. I have had the same issues you have and have resolved these and more and they have all been to do with IE. The schools we support do not have another browser to use as it is policy ONLY to use IE so we have had to "fix" them.
Several calls to SW support has them blaming Microsoft, which may be true. Firefox doesn't present with these problems, but I cannot force all of my users to switch to firefox. Am I the only one having these issues?
What you need to remember is that out of the box "by default" the network garudian install is restrictive, this is by design and will need tweaking to get it right for your school.
Yes it's easy to install, and do basic configuration but you do need to spend some fine tuning.
Shout if you need anymore help :D