I found out that Defensewall had stripped my administrative privileges - even after I exited DW. I'm running XP Pro SP3 with a single user, so I was backed into a corner. I was worried for a few minutes that my system was hosed, because I wouldn't even be able to perform a system restore. I used MSCONFIG to stop DW from running the next time I booted, and it complained that I didn't have sufficient privileges. But fortunately, after a reboot I was able to uninstall DW and now my system is back to normal. Note to self: be careful about installing security software without a very recent backup.