Make sure they are all in their own folders... like the .toc file (and most of the rest of the files) that come with each of them should be in (for example)
C:\Program Files\World of Warcraft\Interface\AddOns\PiggyBank
Make sure its not in:
C:\Program Files\World of Warcraft\Interface\AddOns\Interface\AddOns\PiggyBank
or
C:\Program Files\World of Warcraft\Interface\AddOns\Addons\PiggyBank
Hope this helps! Also, try reading the
FAQ and
Cairenn's excelent post.