I have connected a laptop HDD to my desktop via a USB cradle.
I can navigate all the directories and read all the files except in the User folder, which is where all the files I need to access are stored.
How can I access these files and folders?
You need to take ownership of the files, probably.
In XP right click on the user profile directory and select properties. Go to the security tab and click the Advanced button. In the Owner tab, select your username and check the box Replace owner on subcontainers and objects. Press OK. Press OK again. Let the system process the files and then go ahead and move into the directories.
You may need to be in safe mode to access this, or if you are using a Home edition of the OS you may not be able to do it at all.
If you're in Windows 7, the process should be essentially the same, but I don't have my Win7 box in front of me and so cannot tell if any of the dialogs look different.