Plus! Settings
Go to Plus > Preferences..at bottom left you will see Import/Export, choose export to save your preferences to a file (the wizard will help you through that). Save that file to a disk and import them by going there again..just this time choose Import.
Plus! Custom Sounds
Open the soundlibrary from Plus! in the menu or the Plus! icon in main Messenger screen. At bottom left you will again find Import/Export, Choose Export to create a soundpack of the sounds currently in your Sound Library (a wizard will help you here aswell). Save the soundpack to disk and import on your new computer by goin to the same again...just choose import this time.
Instead of going to the menu to import those files you can also doubleclick them.
Custom Messenger Content
Get
MSN BackUp and install this on both computers, this program will also backup backgrounds and dynamic content. Run it on your old computer to make backups. Now move these backups to your new computer and run the program on that.