I have created a transport rule in exchange 2010 so attach disclaimers to emails. Is it possible to make this disclaimers visible in the newly created email before it is sent?
Transport rules only apply as the email goes through Exchange. It doesn't apply before. If you want something to show in the email then you will need something client side.
Most third party disclaimer/signature management tools work in the same way - applying the text after the email has been sent.