If you're planning to upgrade to Vista soon and have a mind about security, there's a fairly good piece that goes over security in Vista, and how it relates to Windows XP. It covers the default types of user accounts, IE7, the built in anti-spyware mechanisms via Windows Defender, parental controls and a few other things. It doesn't go into any technical detail, but is a good over the top glance of what you can expect out of the box from Vista.
Particularly, for a moderately experienced Windows user, the UAC has been the biggest gripe. While annoying to many, it is probably the biggest step towards making the typical home PC safe, rather than a haven to zombie bots and malware.