if you are using XP 2000.
click on start,click on settings,click on 'performance and maintenance'. In the upper left hand corner of the window you will see "system restore" click on it. A window will open. Click on 'restore my computer to an earlier time' then click 'next'
Another window will open showing you a calender on which you can choose a date to which you can restore your computer's settings. Try the day before your mate installed the firewall.
Then follow the instructions and hey presto the firewall will be gone.
fantazum, October 2005