Thanks guys - that takes me back. I'm not sure what structural modifications we can make to exactly mimic that. I will say though that the initial PM page is pretty similar (while it shows content of a PM at the top) it shows a list of PM's below that (like the vbulletin one).
Additionally, if you'd like your old replies to be saved then simply hit the "quote" button instead of reply. If I'm hearing what some of you are saying, you'd like the "reply" to just "quote" everything anyways?