If you get as far as reinstalling Windows, make sure that you use a 'repair installation' (otherwise you'll reformat your hard drive, with the loss of everything that's on it).
Instructions for XP are here:
http://www.microsoft.com/windowsxp/using/helpa ndsupport/learnmore/tips/doug92.mspx
(That page includes the instruction "Configure your computer to start from the CD-ROM drive". It's quite likely that simply putting the Windows disk into the drive, and restarting the laptop, will do the job anyway)
As usual, Microsoft have made a simple task harder when they've 'upgraded' Windows. Vista doesn't have a 'repair installation' option, per se, available. (Some sources tell you to use 'Upgrade Install' but you have to have loaded Windows fully, in the first place, for it to work!). This
might help:
http://vistasupport.mvps.org/windows_vista_rep air_options.htm
Chris