I do exactly what you want to do. When I set up the device's partnership with my computer I chose "overwright items on this computer with items on the device" That might be a place to start... I have Active Sync though, so if you are Palm based, I have no idea.
Yes, same option exists for Palm HotSync. There is a one time option for which device will "push" its data to the other. As with any conversion, there will be issues when your e-mails are too long. But since you are going from PDA --> laptop, this would have already happened when you did the laptop --> PDA sync.