Can I ask is the following what you need to do to soft load Mountain Lion in the 1.1 Macpro after installing ML?
http://m.wikihow.com/Run-Mac-OSx-in-64-Bit-Mode
Tutorials and logic for installing Mountain Lion on MacPro1,1 (your machine):
http://forum.netkas.org/index.php/topic,1123.0.html
http://www.j4mie.co.uk/blog/2012/02/18/how-to-install-mountain-lion-on-macpro11/
http://www.jabbawok.net/?p=47
https://forums.macrumors.com/threads/1325709/
Some useful videos maybe? http://www.google.com/search?q=how+...a=X&ei=6J1xUYu-G8yLkwXc7IDADg&ved=0CAoQ_AUoBA
Some of these seem pretty elaborate and involved but they'e really not that bad when you consider the overall. For example I could easily make something simple like just opening a door into a complex looking 50-step tutorial with long paragraphs explaining the physics and mechanical details - but in the overview it's a fairly simple operation - especially after you have done it once.
Installing ML on MP1,1 is the same kinda thing. The involved details are there so that your 1st time thru you can proceed with a sure foot. But it's really just: Do this, that, and the other thing - and it works.
PS: This is coming from a guy who has NOT tried it yet, me.