This is purely for my own personal reference as its a bugger of a thing to find a solution to when you have the problem.

The issue I had was with GRUB dual booting linux + windows (+OSX), which should never be difficult. The problem came about apparently because linux is on the primary drive while Windows the secondary. The error received when booting a ‘standard’ GRUB configuration is this:
“Filesystem type unknown, partition type 0x7″
When I say standard I mean somethng like the following:
title Windows XP Professional
root (hd1,4)
savedefault
chainloader +1

The fix is to change the GRUB setting to the following:
title Microsoft Windows
map (hd1) (hd0)
map (hd0) (hd1)
rootnoverify (hd1,0)
savedefault
makeactive
chainloader +1

Which makes sense I guess, but I still think its an unnecesary step.