No AV or firewall
No there's a brave man.... You may not have any sensitive information on the computer but it would be very easy for someone to install a trojan on your pc and use you as a spam relay or worse download nasty files of the web. If the activity is tracked then it is you that will be held responsible.
Sorry to preach doom and gloom but you realy
DO need to install at least an antivirus software package ! There are loads of free packages - Try here
http://www.cableforum.co.uk/board/showthread.php?t=6152