Slava,
Right now the combo box in the Options dialog isn't persisting the setting to your config file (although it will soon). What it *does* do is set the value of App.DatabaseMgr.DatabaseSetKey to the selected database key. This is a static member you can retrieve from anywhere in your code.
Regards,
Kevin McNeish
Eight-Time .NET MVP
VFP and iOS Author, Speaker & Trainer
Oak Leaf Enterprises, Inc.
Chief Architect, MM Framework
http://www.oakleafsd.com