Stop using POP. You're describing an issue that Exchange was made to solve
and that is central storage of your message content. Use an Exchange
account with offline folders if necessary. Your mailbox on the server
should hold the content, not your various clients.
In addition, POP does not recognize tasks, calendar items, etc. It doesn't
even grasp subfolders beneath your inbox.
Get into the 90s and move up.
From previous posts, I see an indication that you use OWA, so you know the
benefit of an Exchange-based mailbox.
After that, I am sure some people are stuck with an old standard protocol
for client access. IMAP will at least allow your clients to synchronize
email content independently with the server and see the same information.
Messages will be stored on the server and your clients (laptop and PC) will
both synchronize to that and not each other.
Finally, if you are still stuck:
Synchronizing Outlook on two machines
http://www.slipstick.com/outlook/sync.htm