I've just downloaded Homm 3 but when it launches it asks for the Shadow of death cd to be inserted. Without it a new campaign can't be started.
I don't think the other problem on this forum relates as I'm installing this on a brand new comp, no previous Homm installs exist... The intro movie is there and everything it just gets to the main menu and restricts me from starting campaigns untill I insert the cd.
Any help would be much appreciated.

The intro is unskippable only the first time you run the game. Now about your cd required problem I've no idea, sorry.

Yeah the intro isn't a problem.....

Did you try reinstall the game and such basic actions?
If yes, then I suggest you should contact GOG support, because I have no idea about it, my Heroes 3 works fine.

Yup, I'm having the same problem here.

I installed the game on a portable drive and it has started working fine.... Wierd though I don't know why it doesn't work on my net book's hard drive.

I had exactly the same problem.
But I Solved it, by running the game as Administrator.

Has anyone tried my solution? Has it helped you?

I had this problem - this solved it. However, I think the key here is what user it's run at - ie. it solves the original problem of having a previous (uninstalled) install because the uninstaller doesn't clear out the registry properly. The CD version stores it's registry data under individual users, so making a new user (or using Administrator) would solve the problem. Not sure if it'd help for the original poster if he had trouble on a clean machine...