I will just add that Norton, which you will have with bt connection is not really free... Just 1 year subscription in best case will be free - after a year you will have to spend around 25-30 pounds to renew licence.
If you want to know my opinion - best firewall is always physical router - you can get ADSL one (which will be fine for BT connection) for around 45 pounds:
http://www.ebuyer.com/UK/product/116446
I'm using 3Com routers from around 2 years - had one also in my cyber cafe back in Poland - they are working perfectly and you can split your connection between 2 or more computers - wired or wireless connection. To wireless one you will obviously need wireless card and little knowledge about configuring 3Com to work with cards - manual is clear enough to get through.
About antyvirus:
There is no such thing as perfect software antyvirus - but technicians knows something, what is really close to be perfect *grins* It is recovery card.
http://cgi.ebay.co.uk/HARD-DRIVE-DATA-RECOVERY-RESTORE-CARD_W0QQitemZ110052137898QQihZ001QQcategoryZ16178QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
First you split HDD to at least 2 partitons using partiton magic or other program to do so. Then you installing clean system and all programs you really need (Office etc.) Then you install software to this recovery card, put it onto you PCI slot, set card to protect disc C (where your system and improtant software are installed) and then you can do whatever you wish - visit porn site, download viruses, delete system folders, mess around in all windows till computer will crash completely. After releasing all steam and hate towards Microsoft you just simply reset your computer and everything is like it was at time, when you put your C partiton to secured mode. Sounds nice? Works even better - my friend using this from 2 years - he just update system from time to time (yes you can remove security temporary). I used it in my cyber also - never had to reinstall system on any computer. It is resistant to any kind of software, only way to kill this card is prolly to burn it using electricity or fire Total cost? 45 pounds for router (multiply connections, no need to connect using some crap BT software cuz router is 24/7 on anyway and autoreconecting in case of trouble - also working as a firewall) and 12 pounds for recovery card (best antyvirus you can get).
Enjoy
PS. Gee, I know crap about Supras, but i love computer topics