In case you were wondering, yes, you can use Monad for your logon scripts.  You can’t just assign a .MSH file as a logon script however, since only file types with file associations work as logon scripts.  Monad installation doesn’t create a file association “.MSH -> msh.exe -command %1” for security reasons.  The best way to run a Monad logon script is probably to create a .CMD file containing “msh.exe -command mylogonscript.msh”.

[Edit: Monad has now been renamed to Windows PowerShell. This script or discussion may require slight adjustments before it applies directly to newer builds.]