Fixing MediaDirect Broken MBR

So I have a brand new DELL XPS M1530, which has Vista pre-installed, and also comes with MediaDirect. Its been working good for about 2-3 wks, until today, whilst doing a normal power cycle to install some software, I inadvertently pressed the MediaDirect key (the little button with the house on it, just left of the power button). Now, before now, I had no idea what that button was. I'm still not sure what it is supposed to do, other than the end result was IT MADE MY SYSTEM COMPLETELY UNBOOTABLE!

It turns out (as I suspected) that when you boot your system with the MediaDirect button, one of the first things it does is "muck up" the MBR. The details of the mucking varies by MediaDirect version, happily the one I have doesn't have the HPA (Host Private Area, wossname), it just has MD in a logical partition.

Half a day later, after much Google searching for an answer, and two unsuccessful calls to Dell Technical Support (both of which concluded that I needed to completely reinstall - but that's their answer for everything, know-nothings that they are, although in the process I found out that my Dell OS Recovery CD doesn't work) I stumbled across an uber-simple solution in the comments of the post at http://www.ideastorm.com/ideaView?id=087700000000BCvAAM, which is so useful I'm repeating it here in case that page gets lost.

For the technical savvy, the "fix" for this particular version of MD "broke my MBR" issue, is simply to make the MD partition inactive (clear the "bootable" flag). For everyone else, here is how to fix it from Linux fdisk (if you don't have a Linux boot CD handy, the Gentoo minimal install CD will do the trick, and is pretty small):

(copied exactly from a Nov 4 2008 comment by esalvador)