Go to the Messenger Plus! Preferences window (Plus! Preferences) and click the "Save/Load" link in the bottom left hand corner. Then select "Export my preferences to a data file" and hit next. On the next page select a file to export to and make sure the "Export contact specific information.." box is checked and hit next. Now backup the file you just exported and use the same method (except this time select "Import my preferences from a data file" instead) to load them
edit: hmm bit slow.. but i was more detailed =P