How do I install to a different drive? Steam won't allow it.

[Fjordmonkey]

What Uther said is the only way. What you can do is copy your Steamapps-folder to another drive, uninstall Steam, reinstall steam to the new drive and copy Steamapps into the new install-location. You might have to verify the integrity of the game cache after that. (go into your steam library, right-click IL2 Sturmovik: Cliffs of Dover, choose properties, go to the Local Files-tab and hit Verify integrity).