Windows Live Messenger using all my CPU

Hey,
I'm running Windows XP Proffesional OS.
Everytime I start-up Windows Live Messenger, it takes up 100% of my CPU,
making my computer very slow.
I have to go to Task Manager and end the process, uninstall it, and install
MSN 7.5.
Any idea why it's making my computer so slow - and is there anyway to fix
the problem?
Thanks in Advance,
Josh