Did a little looking at active processes, and they all added up to little more than 300MB. Again, wtf?
Started killing off everything one by one - Outlook Express, then all Internet Explorer windows, then all Windows Explorer windows, then AIM... still got more than a gig of swap file active. Hasn't made a dent. Tried to close Windows Messenger - it blinged pleasantly at me and kept telling me that it couldn't be closed because Internet Explorer or Outlook Express was using it. Which was bullshit. So I killed its process from the Task Manager - BOOM, there we go, the total commit charge drops to well under 300MB.
In less than ten days, that "Messenger" piece of shit leaked a GIGABYTE of memory... and managed to do so when I wasn't even USING it. (I was signed in but "away" and sent and received no messages whatsoever during that time.) Even more disturbingly, although it was occupying more than a gigabyte, XP's Task Manager only reported about 8MB as allocated to the process.
Greeeeeeeaaaaat. Another outstanding coding job on "A core XP technology!", Redmond.
Update: I just now discovered that although Messenger whines frantically and says you can't close it if you're running Outlook Express because OE neeeeds it... Outlook Express still runs just jim-dandy FINE if you manually kill off Messenger from the Task Manager. Interesting. More of the usual Microsoft "they'll use it if we convince them they can't get rid of it" marketing techniques, I suppose... like when they stroked their chins and told the Department of Justice that Internet Explorer "couldn't be removed" from Windows 98, at which point a SINGLE INDIVIDUAL without access to the Windows source code promptly jumped in and diked it out. (See http://www.litepc.com/98lite.html if you're not already familiar with what I'm talking about re:removing Internet Explorer from Windows entirely.)