- Before anything take backup of your VISTA on DVD media.
- GO to BIOS and set "DVD rom" as a 1st boot device
- Put XP cd and installation will start.
- If still problem persists remove DVD rom from the bay & fix it back ( Caution : while doing it remove battery pack & disconnect everything, turn off laptop )
Last & best solution would be > Download "G Parted" live cd iso. Burn it, Boot your laptop uisng that live CD, partitioner whill show current partition cheme, delete VISTA partition , reboot your laptop and start XP installation.
All the best,
Regards,
Amey.