There is a little known Server Selection Feature in WDS in Windows Server 2008 R2. Its not documented, it's not supported by Microsoft. But its very useful for lab and test scenarios...
How to enable it? Simply go to HKLM\SYSTEM\CurrentControlSet\services\WDSServer\Providers\WDSPXE\Providers\BINLSVC and set AllowServerSelection to 1.
Then restart the Windows Deployment Service. After doing this you get the option tp press F11 and the PXE client will now discover local PXE Servers and allow you to select which one you want to use.
Here are some Screenshots of the feature:
Image 1: Initial PXE Boot Screen
Image 2: The discovery process
Image 3: Selecting the server