You do realize that you haven't asked a question, don't you?
Posting guidelines for how to ask a question
You have stated something that you want to do. Ok. Go do it. You don't have to ask permission.
On the other had I *do* have a question. What good will an Open*FILE*Dialog do for you if you do manage to modify this
sealed class to only show only *FOLDERS*? Personally, I think I would use a FolderBrowserDialog for purposes where I only wanted to see folders.
Of course, that's a sealed class too. So you can't modify it or even use it to device a new class that you could modify. So if you are married to the idea of filtering the folders it displays, you'll have to create your own dialog from scratch.