In order to deploy Windows 7 using MDT 2008 Update 1, you have to do some modifications... documented right here...  :)

Shorthand story is that you need to do 3 small changes in MDT 2008 Update 1

1.     ZTISupportedPlatforms.xml needs a definition for the new Platform Type:

<SupportedPlatform name="All x86 Windows Seven">
<Expression><![CDATA[SELECT * FROM Win32_OperatingSystem WHERE Version like '6.1%' AND OSType=18 AND ProductType=1]]></Expression>
<Expression><![CDATA[SELECT * FROM Win32_OperatingSystem WHERE OSArchitecture like '32%']]>
</Expression>
</SupportedPlatform>
<SupportedPlatform name="All x64 Windows Seven">
<Expression><![CDATA[SELECT * FROM Win32_OperatingSystem WHERE Version like '6.1%' AND OSType=18 AND ProductType=1]]></Expression>
<Expression><![CDATA[SELECT * FROM Win32_OperatingSystem WHERE OSArchitecture like '64%']]>
</Expression>
</SupportedPlatform>

2.     Unattend.xml template file must be modified. All the paths under <DriverPaths> must exist, simple fix is to remove the other lines (marked yellow).

<DriverPaths>
<PathAndCredentials wcm:keyValue="1" wcm:action="add">
<Path>C:\Drivers</Path>
</PathAndCredentials>
<PathAndCredentials wcm:keyValue="2" wcm:action="add">
<Path>X:\Drivers</Path>
</PathAndCredentials>
<PathAndCredentials wcm:keyValue="3" wcm:action="add">
<Path>D:\Drivers</Path>
</PathAndCredentials>
<PathAndCredentials wcm:keyValue="4" wcm:action="add">
<Path>E:\Drivers</Path>
</PathAndCredentials>
<PathAndCredentials wcm:keyValue="5" wcm:action="add">
<Path>F:\Drivers</Path>
</PathAndCredentials>
</DriverPaths>

3.      Change ZTIUserState.wsf to support Hard Link Migration

sBaseArgs = sBaseArgs & " /config:""" & sUSMTPath & "\" & sXML & """"

                        Else

      oLogging.CreateEntry "WARNING: Unable to find specified USMT migration XML file " & sXML, LogTypeWarning

                  End if

                  End if

      sBaseArgs = sBaseArgs & " /hardlink /nocompress“

If bEstimate then

            oEnvironment.Item("StatePath") = sLocalStorePath

            oEnvironment.Item("USMTLocal") = "True"   

            sBaseArgs = sBaseArgs & " /hardlink /nocompress"

                  Else

                              oEnvironment.Item("StatePath") = sNetworkStorePath

                        End if