Hi, I'm assuming from your query that you are on a work computer or similar, as you mentioned network manager and work places generally like the idea of taking away distractions from there employees.
While the method I will explain is legal, at least in Australia any way, it is not totally ethical and you may in fact be breaking company usage policy by doing so and put your job in jeopardy.
Basically the easiest way around it is by using a proxy, or in some circumstances not using a proxy.
I do not use windows or mac for that matter so i do not know my way around Safari or IE.
however first step for Firefox 3.0.11 on Fedora core 10 goes like this
->Edit>Preferences
Advanced Icon
Network Tab
Under connection click on the settings button
In here it will tell you (and the browser for that matter) how you connect to the internet
by default it is on 'use system proxy settings'
if it is on anything else like use manual proxy, its real easy
if your system uses a proxy you will have to change that. For instructions on this you will need to google something like system proxy settings xp windows and follow there instructions for that.
If your system does not use a proxy and your browser does not use a proxy, you will have to set up an account at a free proxy service site, Google free proxy for a list of major free proxy providers. However if your network admin is anything more than a two day novice they will have blocked most if not all of these on the network as well. Network admins subscribe to lists of known proxy sites and other security threats to make there life easier. If this is the case you will have to set up your own proxy web server and that is getting complicated
However the basics of setting up a proxy are, find one, register, adjust setting within there site, then go back to your browser and input the details such as URL port number. And you should be in business.
The other way which i would recommend is talking to your boss/supervisor and see if you can get FB, hotmail, youtube privileges for 1hr per day between 12 and 1 (ie. lunch break) they will probably be accommodating, Then the Network manger just has to set up a Cron job at the specified times changing restrictions for your username, and back again. That's fairly easy stuff once he works out the command as it will probably be quite lengthy.
Sorry i couldn't be more accurate, while i would be able to get around it, I do not have a box running windows, only FC10 and OpenSolaris so i am very unfamiliar with Windows