Hi,
Use the books in link below for preparing for exams as Microsoft Press Books provide complete knowledge to clear all your practical as well as theoretical concepts.
70 - 680
http://www.microsoft.com/learning/en/us/book.aspx?id=13911
70 - 686
http://shop.oreilly.com/product/9780735627178.do
70 - 685
http://www.microsoft.com/learning/en/us/book.aspx?id=13917
For videos you can type the exam number followed by "video trainings" for example "70-680 video training" and you will get loads and loads of free as well as paid videos to learn as per your requirement.
For difference between two exams 70-686 and 70-685
70-685 tests advanced skills in day to day end user support for Windows 7 and applications running on Windows 7 (Customer Technician Oriented)
70-686 test skills in Planning Windows 7 deployments, Deploying Windows 7 (including deployment tools),
and planning and automating migrations to Windows 7 from earlier Windows versions. This includes things like Hardware Lifecycle planning etc. (Corporate Environment Oriented)
Please mark as answer if this helps you or unpropose as answer if it does not help you.
Thanks
Rehan Bharucha - The Tech Robot
MCTS, MCITP, MCPD, MCT, MCC