A couple of things you could try before we get to deleting things.
HOW TO: Take Ownership of a File or Folder in Windows XP (Q308421)
How To Reset Security Settings Back to the Defaults
Any deletion on in use System folders will probably have to be done outside of the loaded Windows install.
You could try Recovery Console, a parallel install of XP or similar, or even moving the drive to another machine.
You could try deleting from Safe Mode or use this free program.
DelLater.
HOW TO: Install and Use the Recovery Console for Windows XP (Q307654)
An easy to follow recovery console description when unable to start computer due to corrupt registry.
This is a layman's version of Q307545 in simple language.
You might be able to make use of BartPE (a mini XP self contained on a bootable CD and run from CD).
The same might be possible with a parallel install of XP.
266465 - HOW TO: Perform a Parallel Installation of Windows 2000
You can do the same with XP. Don't install any unnecessary programs just some virus scanners, keep the parallel installation as simple as possible.
Or the paragraph in this article.
"To install Windows XP to a new folder (to perform a parallel installation):"
How to install or upgrade to Windows XP
With so much corruption it is worthwhile considering backing up your valuable data and doing a format and clean install of XP