+1 on the Ad-aware. I've tried both the freeware and bought versions; get the full version from Best Buy, it's so worth the $30 freedom from headaches. Webroot Spy Sweeper is another decent one, not as good as Ad-aware, though.

For firewalls, I've always done a different setup from you Andy. I have a Linksys wired router (with built in firewall). I setup a cheap piece of crap old system on port 1, and all pings, cookies, etc. see that. If it dies, no big deal, it's worth maybe $50. Installed on the back are multiple NIC cards, that outsource the connection to my other equipment; my laptop, server desktop station, and my XBox360. The connection is a little slow (only really notice it when you're doing some hardcore downloading), but the hardware I'm really concerned about is safe, because any downloads are put onto the old crap system, where antivirus softwares just rape the hell out of them to ensure they are safe. Of course, my laptop and good desktop have firewalls, and AVG antivirus on them as well, just to be safe. The point is, from a network side, the only thing seen from the other side of the router is the old crap system, none of my good stuff.

And as a further step, I use Norton Ghost utilities. This is a program that allows you to create an image of your computer onto a CD or DVD. So, if your system crashes or becomes virused, whatever, just format the hard drive, restart the system with the disk in the optical drive, and it rebuilds your system for you. It's a fantastic piece of kit.

Some of you may think that's extreme, but with all the viruses and wannabe hackers out there nowadays, I'd rather be safe than sorry.