P5WDG2-WS Pro vs P5W DH Deluxe

I think the P5W DH was some sort of refresh with Conroe support I would go for it.

No difference for Vista though
 
The WS pro was a refresh of the reg WS board, the pro version supports conroe.

My guess would be the WS board because of its intended use as a workstation board, most likely more stable the DH series of boards and will probably overclock better.

I'm not exactly sure, these are just assumptions, maybe someone else can fill in the blanks.

HTH