On the questions in that other thread, ubizmo, the blackberry does not send and receive email in the conventional sense. Unless the data network is turned off, email is delivered to the blackberry automatically. One can access web email (say Yahoo) via the browser or, in the case of Yahoo, via Yahoo Go!, but there's no point with a blackberry as it's more convenient to use BIS internet email setup.
I'm not aware of a way to create separate email folders, except I have read here of separating BES email with an after-market app. Otherwise, there will be separate foldes for each email account you have created in BIS. And all email will also appear the messages folder which contains all messages (SMS, MMS, PIN . . .).