If you ever get the yellow infobar at the top of your contacts list, it does mean that you need to upgrade to the new version. Yes, there is a newer version of "7.5".
To check your version, open MSN Messenger, then up the top, click Help and then About MSN Messenger. After where it says "Version 7.5", read what the build number says.
If it does not read "Build 7.5.0322" then you need to update it. Download MSN here.