The Internet Explorer team described how to slipstream IE 8 Beta 1 into a Windows Vista or Windows Server 2008 image using the process described at  Here's the same basic process with MDT 2008:

  1. Download the needed version(s) of Internet Explorer 8 Beta 1.
  2. Extract the updates from the downloaded self-extracting installer files (into separate folders if you downloaded both platforms in step #1).
    x86: IE8-WindowsVista-x86-enu.exe /x:c:\temp\ie8x86
  3. x64: IE8-WindowsVista-x64-enu.exe /x:c:\temp\ie8x64
  4. Import the IE 8 updates into Deployment Workbench (right click on the "OS Updates" node and choose "New") by pointing it to the subdirectories you created above.
  5. Deploy an OS :-)

Here's what the updates look like in Workbench: