well shy look at it like this... using your office machines to chat when you should be working is generally frowned on by most UK bosses. The sysadmin at your place may be a little pissed if you're using machines under his/her care for your own purposes during working hours (remember they are not YOUR resources, they are the companies)... and has thus blocked access to the chat program.

if you're only using it through your lunch break etc then I don't see a problem with you asking the sysadmin to unblock access... why can't you ask your sysadmin? Is he/she really that much of an ogre?

No one here is going to tell you how to bypass the company firewall and i certainly won't - the best thing for you to do is talk to the sysadmin and be real nice to them or just grit your teeth and learn to live with it. Remember it's abuse of company resources that leads to situations like this.

Z