I know I can create and share a VM between both Mac and PC (same machine technically--my Mac Pro with both OS X and Boot Camp) using Parallels, VMware or VirtualBox (all of which I'm a paid user for sans VB of course since it's open source) and there's even a related SU question here about exactly that, BUT... no one seems to have/give any insight as to HOW to do it (i.e. which file system to put it on, how to actually configure the VM to be usable by both, etc.) Sure there are several articles about copying the VM from one host OS to the other, but that's not what I want. I want to share the image between host OSes so whether I'm booted in Mac or Windows, I can get to my Ubuntu install from either.
Also, of the extremely few articles I did find (even on here!), they all talk about having to change the config of the VM (meaning the VM file's settings like image file locations, etc. and not things like the VM's virtual hardware) but if you change that on one, then you've 'un'changed it on the other, so that doesn't work either, or at least not as they say.
So in short, I want to install Ubuntu in a VM that I can run from either PC or Mac. I don't want to dual (triple) boot, I want to use a VM.
So.... I have a Mac Pro with dual quad-core processors and 16 GB of ram so I want to run the 64-bit version of Ubuntu. I also have two dual-head NVidia 8600s so it's not the stock ATI cards found in most Mac Pro's in case one has better video support than the others.
As for storage, I have two internal 1 TB drives and two internal 1.5 TB drives, one each is NTFS and one each is HFS+. I have an external 1 TB pocket-drive that I can use as well (I can reformat in whatever, including Fat32.).
FYI, I have Paragon's HFS+ drivers for Win7 as well as their NTFS drivers for Mac so reading/writing all partitions from either OS is not an issue. (They even claim native speed via their drivers.) Of course both OSes natively support Fat32 (re: that external drive) albeit there are the size limitations with that in that no files can be over 2GB in size so I'd have to fragment the image into 2GB chunks, which again, I believe they all support. However, that seems like the best format to use if I go external since I can read it no matter where I plug it in, drivers or otherwise.
So all of this said, what's the best way to share a VM image of Ubuntu across my OS X 10.6.4 partition and my Boot Camp/Win7 64 partition both on my Mac Pro? ...and better yet, has anyone written or even found an article showing how to do that? searching has turning up nothing for days. (i.e. Google is decidedly not my friend here!)