If your hives are corrupted then there is only one way out unless you had a back-up of your registry from before they went corrupt.
You might have to remove the hard drive from this computer and install it in another computer as a slave drive and after it is able to be accessed by Windows on that computer you will have to manually backup all of your important data that you have to another media like CD-R's, DVD or Thumb drive. Then when this is done return it to the original computer as a master drive on the primary IDE cable and do the following:
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Microsoft KB - How to perform a clean boot in Windows XP = http://support.microsoft.com/default.aspx?...kb;EN-US;310353