I have an external drive (with disable write caching), but windows really doesn't appreciate having me disconnect the drive without first requesting to safely remove the hardware. fine. But occasionally, various system task tray icons disappear on my system (how annoying!).
the real problem here, is that this includes the 'safely remove hardware' icon. look up the help files on the proper, or alternate ways to disconnect hardware -- they all point back to the icon (seems there's *no* program to run to get at that). so -- no tray icon, you're out of luck!
here's how to launch the 'safely remove hardware' dialog without using the tray icon in XP.
you need to get to the properties sheet for the 'device', if you can see the drive in explorer, you can start from there, if not try this...
open up system properties (right lick my computer, or hit windowskey+break)
choose hardware | device manager.
go to the hardware device you're attempting to disconnect.
right-click and select properties on the device.
select the 'policies' tab.
under the optimize for quick removal section, select the highlighted link 'Safely Remove Hardware'
that should bring up the Safely Remove Hardware Dialog, and you can select the item you are attempting to remove from there. this tends to re-enable the icon in the task tray as well.
look a little further and you might notice the dialog runs under the rundll32 host, so not terribly surprising microsoft hasn't written an application to launch the dialog. clearly an oversight, they've assumed you can always get to the tray icon.