When trying to install the program, I get a warning about an "unknown publisher".

This warning automatically comes out from windows XP whenever you download programs from the internet and the program is not "digitally signed by an established authority". The procedure to "digitally sign" a program is very expensive and not used by mid/small sized companies. Only big companies can afford to digitally sign their programs. Therefore, the majority of the programs available for download, will also show this message.

You can safely ignore that message for our products
that are downloaded from our official download locations.

Whenever you download programs from the internet you should make sure you download them from their original site. For example, you must avoid downloading programs from other users via a p2p file sharing utility.

The "official" download locations for the StarMessage screensaver software is:
http://download.starmessage.gr/starmsg.exe