My self and my brother in law have hit this probelm in Win2K. Contrary to popular information about at boot time having check disk run, well it still told us we could not get exclusive access to the drive to have scan disk fix it.
Something that is little talked about that can allow you to fix it is a feature called recovery console. Baicly it is a text mode that allows you access to your hard drive. You have to login as Admin to do this.
It is on the cd but is not installed, you have to do it your self. You can run it from the cd, you can install it on your hard drive and run it from there, it takes about 7 Meg. of your hard drive for the files.
I installed it on my drive, at boot you have the option of starting recovery console or standard boot. Then you can run check disk on the drive and it will fix the problems and not have anything in the way from windows.
Url to a site that talks about the installing of recovery console.
http//www.cybertechhelp.com/html/tutorials/tutorial.php/id/51
No, I don't know if it exists for XP, never saw anything about it either way.
If you hit the wall like I did, I hope this helps.
Bob