If you were on UN*X boxen, and you wanted to use SMB's Net Send, you could use Filesys::SmbClientParser's sendWinpopupMessage func...
I'm not sure if Filesys::SmbClientParser works on Windows too, Samba appears to...
Altho a plain shell call to net send would probably do the trick

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.