We upgraded to SW2010, and now we are unable to use Workgroup PDM on our Win XP64 machines.

There is a bug that when you use workgroup PDM, and open an assembly it crashes.

This bug is document in SPR 517452 and 518171.  (I haven't seen 517452, but I'm told it applies.)

I was also told that the fix won't happen until SP2.0 (two months)

So, if you use workgroup PDM, and Win XP64, I would recommend that you do not upgrade.

Unfortunately we did...