Here is how it is done...
Create your winpe ISO using whatever method and whatever source you like.
Grab ntldr, ntdetect and ramdisk.sys from a Windows Server 2003 + SP1 source. Replace the ramdisk.sys in your PE ISO with the one from 2K3 + SP1 (if you used a different source for your PE build).
In the root of the target HDD, put ntldr, ntdetect and the winpe ISO. Make sure the name of the ISO is in 8.3 format.... for this example, I will creatively use the name 'winpe.iso'.
In the root of the target HDD, create a winnt.sif file with the following entries
BootDevice = "ramdisk(0)"
BootPath = "\i386\System32\"
OsLoadOptions = "/noguiboot /fastdetect /minint /rdexportascd /rdpath=winpe.iso"
So now you have 4 files on the target HDD, being ntldr (W2K3 + SP1), ntdetect.com (W2K3 + SP1), winpe.iso (any build you like) and winnt.sif.
Now when you boot the machine next, you'll see winpe fly into RAM and you can do anything you like without having to wait for CD / disk reads etc. Go ahead, format c: from within Windows PE... see if windows pe cares!
So now you can use Windows PE for remote server builds by taking a ghost image with the 4 files, booting the remote server off a floppy and dumping down the image, then rebooting. no more waiting for Window PE to crawl across a WAN from your laptop to the target server!