I think WPF is a great solution for your project. There has been many similar apps written in WPF and looks awesome! Some samples can be found at http://wpf.netfx3.com/files/default.aspx, it also contains many other resources and tools to help you to get started. You can also go to WPF homepage on MSDN to get more information and many useful links, such as Hands-On-Labs.
Video playback is fully supported by the platform, there is a Multimedia Overview article on MSDN talks about this in more detail, and there are links in there to navigate you to various objects to use.
WPF apps can be hosted inside IE browser in forms of an Xbap, there is a lab at http://wpf.netfx3.com/files/folders/labs/entry1934.aspx showing you how to create one.
Regarding to database support, I'm not an expert in that area, but I have seen many people using SQL server in their projects, so, I think it works great. If you know what specific scenario you will use the SQL Server for, you can post a question here, I'm sure someone will be able to answer it.
There are also a few things you might want to consider as you make your decision for the project. (1) Media Player 10 or above is required to view video in WPF apps; (2) WPF is not cross platform (works only on Windows); (3) Xbap currently can only be hosted in Internet Explorer, although there are plans to support other browsers in future releases.
If any of your scenarios going to be blocked due to these, a great alternative is WPF/E, which lighter weight and goes cross-platform, but does not contain all functionalities that exist in WPF. You can go to http://msdn2.microsoft.com/en-us/asp.net/bb187358.aspx for more details and samples.
Hope this helps you with your decision making, and please feel free to post any other questions you may have.