I've read through the post lsass.exe Memory Hog (XP Home SP1), although I'm XP professional, and it wasn't the memory hog that bothered me, it is the regular (every one second?) read and write of the hard drive. I can't find "GMT Services." so I can't kill that service.
I've read somewhere of a virus with a lower-case "I" in Arial font, hence "isass.exe", but Windows Explorer (hidden files &* folders) assures me I have only lsass.exe, and it is in the proper place.
I've read http://the-scream.co.uk/forums/t7883.html and used Adminstrative Tools to disable it, but it re-appears after a reboot.
I am tempted to delete lsass.exe by nefarious means, but can't find a definitive statement on what it does, who sponsors it, and what dire effects might befall me.
AFAIK the WinXP automatic updates have kept me up to date as of this morning.
I am uptodate with Grisoft anti-virus, Lavasoft AdAware, Spyware Terminator and Zonelabs ZoneAlarm.