vista + mbr + grub

So you can boot XP and Ubuntu completely, just not Vista?
This is not a grub error or you wouldn't get a Welcome screen.
Vista needs to be repaired. The first step to try is Testdisk
because the second step of using Vista's Startup Repair makes 
some more work of restoring the Ubuntu grub menu to the MBR.

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I borrowed this advice from meierfra about using
Testdisk. sda is the first drive and sdb is the second drive and so on.

"You might try testdisk to rebuild the Boot sector:

Code:

sudo apt-get install testdisk
sudo testdisk /dev/sda

Choose "proceed" on the first screen, then
"intel"
"advanced",
Select the Windows partition (although it should be selected already) and choose
"boot"
"RebuildBS"

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RebuildBS uses a backup of your boot sector. If the backup and
the current boot sector are not identical then you want to use
Testdisk to restore the backup (maybe it says write).

If you have a Vista OEM recovery cd, rather than a Vista install cd
http://neosmart.net/blog/2008/window...disc-download/

bootrec /fixmbr
bootrec /fixboot
bootrec /rebuildbcd