I had following the instructions from the post below - got all the way to installing XP off disc, all appears to be working. After loading all XP program, computer said it would restart and complete installation. Computer restarted, and came to a HALT basically. The message I get: a disk read error occurred - ctrl, alt, delete to restart. Wondering if it's not booting up to correct drive. I have attempted to install XP a few times and get same message. Appears to be when I looked at BIOS. I've read quite a bit that you need to install XP first and Vista last...(not the case, as I have new HP A6142N with OEM Vista Home Premium and just really wanted to see how XP worked on this machine without uninstalling Vista.
Now I can't boot computer up at all. I have recovery drive but unable to get to it. I have back-up with Acronis 10 on external Hard drive, but before I went back in time to my original configuration, I'd really just like to boot up and move on. I've done a lot to on machine since last back-up. I am sure there's a program out there, and some simple answer, but we are talking Vista here. At this point, I would be happy just to delete partition I created with XP and bring it back to Vista as it was. Eventually I may replace Vista with XP, but we'll give it a bit more time (and frustration). The below forum post was very helpful.