I installed the trial of Windows Live OneCare on my childrens machine at home last week - the 90 day trial is available here. If you haven't seen it yet, OneCare can be thought of as an all-in-one tune up and peace of mind package including Antivirus, Antispyware (Windows Defender), a 2-way firewall, a performance tuneup and a backup/restore program. I'm still investigating how it plays with WSUS for the OS updates part... on my list of things to look at.
Note that currently Windows Live OneCare is only available in the US [not that it worries me too much now ;)]. Cheers, John.