Hello. I am writing this to inform others and also in hopes that someone can tell me what is going on. I apologize if it's a bit long. You can just skip to the bottom to get the gist.
I bought a computer with vista preinstalled. From my ubuntu live cd, I resized the vista partition with gparted then installed ubuntu in the free space. Ubuntu worked fine but vista would no longer boot (and it wasn't just a matter of correctly configuring grub). Even putting in the vista reinstallation cd did nothing, just a blank screen. A smart guy on linux forums suggested I stick in my mom's xp reinstallation cd, select repair mode, and then type fixmbr. I tried this, but to enter repair mode required an administrator password and I wasn't able to enter repair mode. I took out the xp cd and tried once more to boot vista normally, and it worked!
I later had problems getting my wireless adapter to work with ubuntu and somehow ended up messing it up so that ubuntu would no longer boot. So I decided to start from scratch and reinstall ubuntu from the live cd, and in the process I decided to change my partitions up and resize the vista partition, again with gparted. After doing this the exact same thing happened: vista would no longer boot and the vista reinstallation cd didn't work. So I put in the xp reinstallation cd, attempted to enter repair mode, was denied, and then rebooted into vista no problem.
Since this happened twice, I don't think it's a coincidence. So I conclude:
1. Resizing a vista partition with gparted makes it unbootable
2. Attempting to enter repair mode with the xp reinstallation cd (though never actually entering it) repairs whatever damage is done by gparted and allows vista to boot.
Anyone know what's going on here?