Hi,
Imaging Dell PowerEdge 2900 have some known issues which are outlined in the document given below,
http://www.symantec.com/business/support/index?page=content&id=TECH110720&locale=en_US
Its recommended to use WinPE as PreOS and add the drivers given in the document given below,
http://www.symantec.com/business/support/index?page=content&id=TECH110257&locale=en_US
Adding drivers to WinPE boot package are explained in the link given below,
https://www-secure.symantec.com/connect/videos/adding-nic-and-sata-drivers-windows-pe
Hope this helps
-Prasanna