Well, the Windows team has finished Release Candidate 1 of Windows XP Service Pack 2, and made it available for public download.  This download is not eligible for technical support, although Microsoft is going to setup some newsgroups (microsoft.private.xpsp2.*) to provide assistance with it.  XP SP2 provides many security enhancements, ranging from improvements to the Windows Firewall, to enabling of the NX bit, which should help to mitigate the risk from buffer overruns.  You can find an overview of the changes in SP2 here.  (One of the more popular ones will probably turn out to be Internet Explorer's new built in popup blocker).  A much more detailed description of all the security changes in XP SP2 is available here.