Blackberry can only handle one BES as far as I know. I'm sure someone will jump in if I have it wrong.
If your Blackberry syncs with BES wirelessly, I don't think you have any options to sync your personal Outlook data from a separate Outlook file. In Outlook using Exchange there is a field for "private" to keep information from being shared. If you aren't using the BES wireless sync, then you can sync information using different folders in Outlook using the Desktop Manager software.
You can deal with personal email using BIS (T-Mobile) or BWC.