Right-click the file or folder, click Properties, and then click the Security tab.
Click Advanced, and then click the Owner tab.
Click Edit, and then do one of the following:
To change the owner to a user or group that is not listed, click Other users and groups and, in Enter the object name to select (examples), type the name of the user or group, and then click OK.
To change the owner to a user or group that is listed, in the Change owner to box, click the new owner.
I,ve pasted the above from Vista's help section.
I'm 99% sure its the same for xp if your using that, try the above and if it does not work just do a search in help and support for "access denied" or "ownership" without the quotes.