The ContentBlock widget has "Flash" manager which browses the file directory ( you need to create Files folder) and you can use it to insert flash on the page.
You can use the RadEditor for ASP.NET AJAX which generates flash out of the box and create a custom button
that opens dialog which browses the Libraries. To browse content items form Images/Documents/Video libraries you can use MediaContentSelectorView.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items