Did you install any DRM software in XP? Or are you running some virus software that thinks grub is a virus?
In Windows 7, had to remove Windows 7 DataSafe.
HP ProtectTools, Dell Recovery, flexnet and a few others write into MBR meierfra.
https://bugs.launchpad.net/ubuntu/+s...b2/+bug/441941
https://bugs.edge.launchpad.net/ubun...1?comments=all
Dell Media direct or Uninstall Dell DataSafe issues with MBR
http://ubuntuforums.org/showpost.php...49&postcount=9
http://ubuntuforums.org/showthread.php?t=923576
New versions of grub work around this issue:
Adobe Photoshop, CAD/CAM, Rosetta Stone, Matlab others
see google search on others with same issue: flexnet site:ubuntuforums.org
Sector 32 is already in use by FlexNet
http://www.amazon.com/Adobe-Photosho...ews/B001EUDGO2
The problem turned out to be Adobe's digital rights management software [DRM]. Do your own search for "FlexNet," formerly known as "SafeCast." What I have read is that FlexNet is a viral rootkit that replicates in multiple locations whenever a CS3 or CS4 product is installed, including trial versions.
Erase flexnet, if not using protected windows software anymore:
http://ubuntuforums.org/showthread.php?t=1661254
Grub2 bug Natty, overwrites windows boot in sector 63, recover backup & chkdsk to fix.
https://bugs.launchpad.net/ubuntu/+s...b2/+bug/730225