I know this article is a little old but it's quite scary as to how fast an unpatched Windows box can be exploited. Unless one has broadband you're stuck on a 56K modem trying to get MB upon MB of patches installed - all the while you vulnerable to exploit.
Last night installed Windows XP SP1 onto a spare laptop and it spent about an hour downloading and installing patches before it was ready for use. Thankfully I've got broadband and am behind a router/firewall so it's not too much of an issue. Damn I'm scared to think of what's sitting on my mom's PC. It's probably been broadcasting spam to the world for ages now ;-)