I have tried trillian, xp messenger, msn messenger and easy message, and all four crash when I start them. any help greatly appreciated. I have used xp-antispy extensively, maybe I tweaked something there?
do a detct errors/repair for M$ messengers. If it's msn messenger 4.7 xx then use xp spy on front page to remove it, then use version 6 of windows messenger. The others uninstall then clean out all setting in registry to them, make sure you save any files you wanna keep. I clean most items in registry with registrar lite, which can be found on link below, then reinstall the messengers again.
I had problems with AIM and MSN crashing recently (and IE), and when I rollbacked my video card drivers it went away for some reason. I was using the newest Nvidia forceware drivers.. so maybe that helps?