The cdosys should work on a windows 2003 server.
but you have to setup the microsoft smtp server for that.
you can install the smtp server from ms from the add remove programs.
than set it up, it should apeer in the iis console and choose a special port to send mails from that, like 2525. don't use port 25 because it's allready used by mailenable.
we have a win 2003 server and cdosys is working well.
chris