On your old machine, did you have multiple user accounts and was each account set to private? If so, the files are only visable to that person. If you still have the old machine or if you just upgraded the drive, reuse your old drive as the boot drive and log in as the correct user, then copy the files to a new folder that is not part of documents and settings (assuming XP). Make sure you reset all teh file attributes and permissions to allow all users to read/write the files. Then when you start using the old hard drive a secondary drive again, you should be able to access all the files.
Hope that helps and is understandable