I have found a workaround in Windows 7 to be able to open files of different types simultaneously:
Download and install freeware ExporerXP:
http://www.explorerxp.com/
Go to the desktop icon for ExplorerXP and open Properties.
Under the Shortcut tab select "Advanced" and then check "Run as administrator"
Under the Compatibility tab select "Run this program in compatibility mode for:" and choose "Windows XP (Service Pack 3)"
Select OK to close the Properties window
Open ExporerXP using the desktop icon
Select multiple files of different types and hit <Enter> on the keyboard (right-click doesn't work)