I too just switched (not by choice) from XP to Windows 7 and had a lot of stuff stored on external hard drive. At first I couldn't figure out how to transfer from external to internal hard drive but then I figured it out. Open two copies of Windows Explorer, minimize them to half size and put them side to side. In one window, open your C drive and create a destination folder. This is where you're going to store the files from your external hard drive. In the other window, open your external hard drive. With the two windows open, you can just drag the files from the external to the C drive and it will copy them over. Once the files are copied, you can delete them from you external drive. I hope this helps.
As far as the permissions stuff, I don't know anything about that.