If you move a message it will not get put over to the BlackBerry.
The ONLY ways to get old email to the BlackBerry is to either use the prepopulation with 4.0 (7 days or 365 messages, whichever is lower) or to backup the messages database on the old one and restore it to the new one before any other messages get there (restoring the database will overwrite the database completely, not add to it).
And the last option is not as pretty, but you still get the message on the BlackBerry, and that's to forward the messages to yourself or copy them to memo pad items. It's an ugly workaround, but if it's only a couple emails and they HAVE to be on your BlackBerry, it works.
BTW, I read at the PocketMac site that they were trying to implement actual email synchronization in future versions. Of course this doesn't help anyone with a PC per se, but maybe they'd be looking into a standalone inbox sync tool?