Hmmm...I|Kevin|I, you could rename the messenger exe to something else, keep the .exe the same but change the name, i.e.- from msmgs.exe to ONEmsmgs.exe, then after you rename it drag a new shortcut or edit the props of the current one to point to the new file name...
Hope this helps some
There are probably 20 different ways to stop it from autostarting, find the one you like best...
/JD