Indeed, it is
1) Install MSNM 6.2
2) Copy the MSN Messenger folder to somewhere else & rename it (for example, 'MSN Messenger 6.2')
3) Install MSNM 7.0
4) Move the MSNM 6.2 folder back into the Program Files folder, create a shortcut to msnmsgr.exe & put it somewhere handy.
If you want to run them both at a time, you need to enable Polygamy.
StuffPlug-NG or
A-Patch can do that.
Note that it doesn't matter if you install 7.0 first then 6.2; you can do it either way.