I've got a very similar setup to the Duck. Only one pc at home so no router just the usb modem.

Avast AV, Adaware SE (1.06), Spyware S+D, Spyware Blaster, MS Antispyware, Zonealarm firewall + another firewall at my ISP and basic filtering on their side for malware sites (I don't trust it but hey it's free). I run Firefox on the PC my GF refuses to use anything but IE so her account runs with reduced rights. Everything is patched up to date and spyware/AV is updated daily and scanned weekly. The machine is switched off when not in use.

I don't allow any email progs to run on the machine I only use webmail.

The only thing of any 'value' on the machine is my GF's files for teaching and I back those up onto CD weekly.
I've never had a virus that wasn't caught immediately and I've not had any reported spyware on the machine for years.