There are several project related panel windows. The main Project Window appears when you View > Panels > Project Window. The Project Window is set up by default as a tabbed container for all the project-related panels, such as the Project File List and Project Symbol List. Each project panel has a tab.
The Project Window can be either docked to a side of the Source Insight main application window, or it can float in front.
As with any grouped panels, you can click on the tab for any project panel and drag it out into its own floating window, or dock it separately.