Hey,
Yes, if Messenger 4.7 pops up and signs in automatically, you got to set
Messenger 4.7's preference to not to load up when Windows starts. If
Messenger 4.7 doesn't load up when Windows starts, it will not sign in for
you and you can use Messenger 7.0 without any interruptions!
To stop Messenger 4.7 to load on every startup,
1. Open up Windows Messenger 4.7
2. Click Tools > Options > Preference
3. Uncheck "Run Windows Messenger when Windows starts"
Once you have done the above, restart your PC and log in to Messenger 7.0.
You will not be receiving any message that you have log in on one place etc.
Hope this helps.