GPT -> MBR Clean install vs. Backup

[RTA]

So after about a week I got my hackbook up and running, with everything working perfectly (except sleep -- but I'm glad that doesn't work). Problem is I've recently gotten into LOTRO, and they don't have a proper mac client. There's a workaround to run it in X11, but it doesn't like my graphics kexts, apparently (9600M GT), as when it loads the screen is all...warped. So I want to install Vista x64 again to take proper advantage of all my ram (6GB), but I stupidly formatted my drive as GPT originally instead of MBR like I should have, because I figured...why on earth would I ever want to run windows again? So to cut a long story somewhat short, I need to reformat my drive to MBR, which is a destructive format. I have drives to backup all my information, but my question is this- if I make a full backup via disk utility (Restore primary hard disk GPT -> secondary disk), can I restore (Restore backup disk -> primary disk New MBR) without problems? Or am I going to run into issues switching between MBR and just trying to restore? I hate having to re-install my OS if I can help it, as it took me a long time to get everything working just right, and I failed to properly document it.