For some Applications you need the NULL-Device, but it isn't installed on Windows XP Embedded or Windows FLP. Here's a tutorial how to install it:

1. First you must have the file "null.sys" in this folder:

%SystemRoot%\system32\drivers

If you don't have this file you can copy it from another Windows installation or from a Windows CD. The filesize is 4,50 KB (4.608 bytes).
2. Then you need some entries in your registry. Download this file:
   

   null.reg

   Doubleclick on it and select Yes.
   
3. If you get an error message you have to change permissions in your registry. Otherwise jump to 5.
   Start->Run...->Enter "regedit"->OK
   Rightclick to this key:
   

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root

   and select Permissions...:
   
   Now give Everyone Full Control:
   
   
4. Now run the file "null.reg" again. You shouldn't get an error message this time. You should reset the permissions now.
5. Restart your PC.

The NULL-Device should work now.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{8ECC055D-047F-11D1-A537-0000F8753ED1}]

"Class"="LegacyDriver"
@="Non-Plug and Play Drivers"
"NoDisplayClass"="1"
"SilentInstall"="1"
"NoInstallClass"="1"
"EnumPropPages32"="SysSetup.Dll,LegacyDriverPropPageProvider"
"Icon"="-19"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_NULL]
"NextInstance"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_NULL\0000]

"Service"="Null"
"Legacy"=dword:00000001
"ConfigFlags"=dword:00000020
"Class"="LegacyDriver"
"ClassGUID"="{8ECC055D-047F-11D1-A537-0000F8753ED1}"
"DeviceDesc"="Null"
"Capabilities"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_NULL\0000\LogConf]


[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_NULL\0000\Control]
"ActiveService"="Null"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Null]
"ErrorControl"=dword:00000001
"Group"="Base"
"Start"=dword:00000001
"Tag"=dword:00000001
"Type"=dword:00000001

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Null\Enum]
"0"="Root\\LEGACY_NULL\\0000"
"Count"=dword:00000001
"NextInstance"=dword:00000001