If you want the version that has the one-way web-cam feature follow this.
1. Start > (In XP, click Run) > Type in the following & press enter:
msiexec /x {B57EAFF2-D6EE-4C6C-9175-ED9F17BFC1BC}
2. Follow instructions to uninstall Windows Live Messenger.
3. Then download and install this version:
http://messenger.jonathankay.com/redir/w3qfe2/wlm.asp
** As said above this is not recommended and might cause problems, I've been running an old version of Windows Live Messenger and personally had no problems. It's up to you. Good Luck