No.
The Mac Pro is not ATX, E-ATX, or BTX. It is a custom motherboard designed for the Mac Pro case and that alone. Since the board itself spans nearly the entire side of the MP casing internally, it probably won't even fit in any standard case as I believe it is larger then E-ATX.
If you did manage to get it into something like a CM stacker- several problems are going to spring up right away:
- None of the components have standard screwholes, you'll need to drill your own
- You will need to have a support structure to hold up the FB-DIMM Riser cards, so they don't snap off the board
- You will need to mount the fans in nearly the identical place that they were on the Mac Pro, using the same fans (otherwise the Mac Pro will get thermally confused and the fans will rev up)
- Your PCI Card slots probably won't line up, you'll need to rebuild those too
If you were building a custom case from scratch with CNC machines and aluminum- maybe this would be possible. Chucking it in a CM case is a no-no, the Mac Pro case is far superior (in most ways) to the CM unit anyways- since the Mac Pro logic board and the case itself were /designed/ for each other. There is no standard that the Mac Pro falls under.
-SC