DUN woes

Arrrrgh...
The Connect dialog for dial-up networking pops up at intervals without being requested by me. I know software is getting smarter and all that, but I don't feel my DUN dialog should be able to decide for itself when it fires up.
Other than that it seems to be working as advertised.
I have a local network linking the offending machine to another, peer to peer, using TCP/IP so I suppose it's something to do with the network.
But what?
Any suggestions would be appreciated. Thanks...Andy.