You need one of two programs to open and decompress a '.SDB' file - Either Panasonic Song Manager or Fred Mellink's KN7000 SD Explorer. Both programs will run on Windows 7.
If you don't have the Panasonic Song Manager (it was included on the 'Applications and Drivers' CD which was included with the KN7000 package) you can download the CD content from my website and burn a CD : http://www.willumspages.co.uk/page10.html Tip #15. The installation procedure is also available in Tip #1.

Fred's program is available here : http://vision-4-life.nl/SDExplorer.htm