Deactivating Outlook window for a custom form

I'm currently writing an add-in where a pop-up box of choices appears when a certain action takes place. I'd like to make it so that the user can't continue in Outlook until they've either made a choice 开发者_开发知识库or cancelled the pop-up window.

I know how to do this for a static windows form-based application but seem to be running into difficulty and few answers (my google-fu is not coming up with anything right now).

Advice and assistance are welcome as always, Larry

Call ShowDialog().