The following is a list of all settings that you can place in a .rdp file. This list is for the mstsc.exe client in Vista. Don't ask me why Microsoft doesn't publicly list all of these, ask them :-)
I created this list when finding out how to do the equivalent of /SPAN in an .rdp file (Span Monitors:i:1). I don't know what half of these do, that's for you to work out with a bit of experimentation and googling.
Louis Solomon / SteelBytes
1/Jul/07
Alternate Shell:s:<string> AudioMode:i:<int> Authentication Level:i:<int> AutoReconnect Max Retries:i:<int> AutoReconnection Enabled:i:<0 or 1> BitmapCacheSize:i:<int> BitmapPersistCache16Size:i:<int> BitmapPersistCache24Size:i:<int> BitmapPersistCache32Size:i:<int> BitmapPersistCacheSize:i:<int> ClxCommandLine:s:<string> Compression:i:<0 or 1> Connect to Console:i:<0 or 1> Dedicated Terminal:i:<0 or 1> Desktop Size ID:i:<int> DesktopHeight:i:<int> DesktopWidth:i:<int> DevicesToRedirect:s:<string> Disable CTRL+ALT+DEL:i:<0 or 1> DisableConnectionSharing:i:<0 or 1> DisplayConnectionBar:i:<0 or 1> Domain:s:<string> DrivesToRedirect:s:<string> Enable Mouse:i:<0 or 1> EnableCredSspSupport:i:<0 or 1> Full Address:s:<string> GatewayCredentialsSource:i:<int> GatewayHostname:s:<string> GatewayProfileUsageMethod:i:<int> GatewayUsageMethod:i:<int> Keyboard Layout:?:? maybe :s:<string> KeyboardHook:i:<int> Negotiate Security Layer:i:<0 or 1> Prompt For Credentials:i:<0 or 1> RedirectClipboard:i:<0 or 1> RedirectCOMPorts:i:<0 or 1> RedirectDrives:i:<0 or 1> RedirectPOSDevices:i:<0 or 1> RedirectPrinters:i:<0 or 1> RedirectSmartCards:i:<0 or 1> RemoteApplicationCmdLine:s:<string> RemoteApplicationExpandWorkingdir:i:<0 or 1> RemoteApplicationFile:s:<string> RemoteApplicationGuid:s:<string> RemoteApplicationIcon:s:<string> RemoteApplicationMode:i:<0 or 1> RemoteApplicationName:s:<string> Screen Mode ID:i:<int> Server Port:i:<int> Session Bpp:i:<int> Shadow Bitmap Enabled:i:<0 or 1> Shell Working Directory:s:<string> Smart Sizing:i:<0 or 1> Span Monitors:i:<0 or 1> Transport Type:i:<int> UserName:s:<string> WinPosStr:s:<string>