Shoutbox

Beware that Pleh's FileSharing plugin is a VB-plugin, this means you have to register the DLL with regsrv32 (as you pointed out) but you also need to add a registry entry for it!!!
Install version 1.2 (to add the registry) and after that unregister the OLD DLL, then replace the old DLL with the new DLL and register it again...

EDIT: I just tested it, it's working fine in Messenger Plus! 3.x with MSN Messenger 6.x