Explorer is consuming more and more memory as time goes by ... and
rebooting doesn't restart the clock.

I've been noticing this for a while, and realized the immediately-
after-I-reboot VM size for explorer.exe had crept up from the original
60 or so MB to around 160. Wondering if the various open windows I
usually had preserved across sessions caused the additional usage, I
closed them all and rebooted. Presto -- fresh session, no open
windows, process size about 170MB. I determined that emptying the
recycle bin makes no difference either. Nor does removing a CD that
had been sitting in one of the trays that I wasn't expecting to need
for a while. In fact, after removing the CD and recreating my usual
windows, then rebooting, I got a fresh, shiny new 300MB(!) Explorer
process.

System is virus and spyware free. I haven't installed anything
recently that includes any shell extensions. Yet something is making
Explorer use more memory each session. At the current, accelerating
rate, it will render this installation of Windows XP unusable in less
than another month, after which, lacking a proper install CD (just a
"recovery" CD that will wipe the HD if used) I would have to take
apart both my computers, move the hard drive to the second, rescue all
important files, move the hard drive back to the first, put the first
computer back to the factory default configuration with the "recovery"
CD, move the hard drive again, copy back the important files, move it
AGAIN, and then pray the cause of the bloat wasn't in any of those
files. And if it was ... binary partition time, and gazillions of
hardware fiddlings, each with a nonzero risk of accidentally trashing
something.

Well, I could also burn all important files to about a billion CD-Rs
and pray they're all readable later, instead, but it would take
hundreds of times as long.

Or, of course, I could simply locate the problem before the clock runs
out and fix it with surgical precision. If I only knew what the
problem was.

So ... What determines the immediately-after-reboot Explorer process
size? The windows it recreates from the last session, presumably, and
the contents of these windows, the desktop, and the start menu. Shell
extensions. And something else, because with all of those things
staying equal, the process size keeps creeping up. In any given
session, it bloats to over 300M over time, and then the system becomes
increasingly sluggish as things are forced to swap, until a reboot.
And the after-reboot size also creeps up. It's now around 300 already
at startup, which means I now won't be able to use anything memory-
intensive at all without sluggishness setting in straight away.