Howto fix grub after converting to reiserfs

[marc <gmane@auxbuss.com>]

Hi,

I have a little problem :-o

Machine has Windows on sda2 vfat, which is the MBR. (sda1 is not used), 
Linux on sda3, sda4 contains sda5 swap, sda6 ext Linux, sda7 is vfat 
shared space.

Here's the story, so far

- moved Linux (on sda3) to a safe place while booted on another 
partition (sda6)
- formatted sda3 as reiserfs
- amended both fstabs (sda3 and sda6)
- mounted the newly formatted sda3 partition
- moved the data back onto sda3
- rebooted.

Grub currently loads from /boot on sda3, or rather it doesn't now. I'm 
getting an error 17 : Cannot mount selected partition. I'm not overly 
surprised, but I'm not sure what to do next.

I can mount the partition from a live CD without a problem, and I 
obviously mounted it from my sda6 partition.

Suggestions welcomed.

-- 
Best,
Marc