There's no excuse for not having a firewall and antivirus software in place these days, especially when you can get AVG Antivirus (ww.grisoft.com) and Sygate Personal Firewall (
www.sygate.com) for free.
Note that these are free for personal use, and you may need to purchase a network version if you want to protect several PCs, but we are not talking £1,000's here.
I'd recommend looking at the latest Email software. Outlook 2003 seems to be pretty good at blocking spam, and also prevents images from downloading unless you've authorised the sender's email address to allow graphics to be displayed.
I'd also suggest speaking to your ISP - they may offer enhanced email accounts which, for a little more, have antivirus and antispam built in. Easyspace (
www.easyspace.com) has this, as does Ultradesign (
www.ultradesign.net) - I pay £300 for 20 email accounts, and had my spam/virus intake reduced from several hundred to just a couple. Their filters can be a little too aggressive sometimes, so you'll need to understand what is filtered. (For example, don't put !!!!! in a subject line, don't email file types that can contain viruses - zip them etc...)
Ask yourself this: If you came into work tomorrow and your PCs were not operational, what would you have to do to get them back up and running again? How long would it take and how much business would you lose because of it? Is there data that you do not have a backup of?
On another note...
I work from home and regularly back up to DVD-ROM, but it's not regularly enough for my liking, and is always a hassle to remember. So when I last upgraded my PC I stuck all of the old components in a case, added a wireless network card and stuck it in my loft. Every night at 2am it backs up my entire hard disc. That way, if a virus should get through or I have a hardware failure I can literally just bring the other PC down, decompress the backup file and start working with the latest data. (It also acts as a very good MP3 server as well

). Any old PC would do for this, as long as you have a nice big hard disc - these are very cheap these days.