Surprisingly, .Net does not ship with a pre-built folder browser that looks like Windows Explorer. You either have to write your own, or use someone else's.
A not-so-nice workaround is to use swApp.GetOpenFileName, which looks good, but the user must select a file from within the folder.
Do you want your folder browser to show you what files are in the folder? You can use GetSaveAsFileName (I think) or GetOpenFileName to browse with files visible. Then you have your user select a file (rather than a folder). Then you just strip the filename off the path returned.
Alternately, if you want to actually pick folders and you don't care about seeing the content of the folder, you can tie in to Office API and use the folder picker of the FileDialog object. You will get an Office style picker.