Browse to old hard drive in Windows Explorer.
Select folder/file you wish to access.
Right click, select "Properties".
Click "Security" tab.
To right of "For special permissions or advanced settings..." click "Advanced".
Click "Owner" tab.
Under "Change owner to:" select the new user ID, and click "Apply".
If it offers the option to apply the changes to all contained folders and files, then do so.
That should do the trick.