You can only move it manually from the desktop.
You could however make a default file/folder on the second drive for all downloads to go into and create a shortcut to this folder from your desktop
In firefox if you select options, on the general tab you will see downloads, if you put a tick in "save files to" you can select a file/folder on any drive. If you go to the file/folder right click and select send to/Desktop (create short cut) this will create a shortcut allowing easy access to the file and downloads from the desktop.
In ie if you go to tools, view downloads, at the bottom left click on options you can select the default download folder