It helps to include links to the instructions you followed. I don't know if they are the same as the ones I have.
turingtest2 post on downgrading iTunes 11 to 10.7 in Windows - https://discussions.apple.com/message/20473745
iTunes 10.7 - http://support.apple.com/kb/DL1576 Select the link after "Download iTunes 10.7 for Windows here".
iTunes 10.7 for Windows 64 - http://support.apple.com/kb/DL1577
To add the songs just use file - add folder to library and point to the folder where thesongs are on your external drive ad theywill be reimported As long as you have the song files geting them into itunes is not difficult. I often delete all songs in itunes but use the option don't remove files and then reimport them after I have cleaned up the directories and renamed them etc. Just never take the option to send files to recycle bin. that reimport works in 10.7 or 11.0