Windows Live Messenger 2009 on Windows XP 64bit
I've made a little patcher for Windows Live Messenger Setups that allows to bypass os check.
Just download a wlm setup (there are many, localized/full blown), then download and run this little utility and patch the setup file, it will make a backup of the original file.
Windows Live Setup Patcher - sources (yes lol I use memmem from libc)