It has to, this is from the readme i have in the zip:
Instructions:
1) Make sure you have plus! build 46
2) Move Uptime.dll to your Plugins directory, usually C:\Program Files\Messenger Plus! 2\Plugins
3) run install.reg (doesnt matter where you run that from)
4) register the DLL, to do this go to Start | Run dialog, and put in
regsvr32 "C:\Program Files\Messenger Plus! 2\Plugins\Uptime.dll"
make sure thats the correct path to the plugin, then hit enter, it should register correctly. Now restart MSN and you can type (!XUP) for the time that your computer has been on.
MAKE SURE You've done all that