[link|http://torpark.nfshost.com/|http://torpark.nfshost.com/]

Torpark is based on Firefox and Tor, it can run off of a USB device, and I think it does not need to be installed. Your surfing will go out over the Tor/Onion network, and I am not sure what your administrators will see, but they cannot block all Tor addresses. You can always ask for a new Tor address.

Still surfing at work is a bit unethical and against IT usage policies, use at your own risk.