This is what you need to do:
1. Extract Setupldr.exe/osloader.exe from XP or W2k3 Source.
2. Customise the setupldr.exe/osloader.exe to your liking.
3. When done you need to type this in the cmd prompt window.
CODE
copy /b stpboot.bin+setupldr.exe setupldr.bin
or
CODE
copy /b stpboot.bin+osloader.exe ntldr
4. Use it in your ISO!
StpBoot.bin can be found
Here.