Outlook 2003 send/reviece very slow with exchange 2007

Our company has about 150 employees, we all use Outlook 2003, and we do not use cached exchange mode.  I am in the process of transitioning from our single Exchange 2000 server to a single Exchange 2007 server.  Mail flow to & from the old Exchange 2000 and the new Exchange 2007 server has been established.  Mail flow to & from the Internet is working correctly for both servers as well.

As a test, I have moved my mailbox and about 10 others to the new Exchange 2007 server and have updated our Outlook profiles on our desktops.  Now Outlook is slow to send & receive for everyone that is on the new server.  When we were still on the old Exchange 2000 server email delivery was immediate when sending or receiving a message to/from someone else within the company.

I have tested by sending mail to myself from Outlook 2003 and this is what I've observed.
1)When sending mail, my Outlook 2003 outbox indicates that there is one unsent message for approximately 60 seconds.
2)After about 60 seconds the message count for the outbox and inbox update and I receive a newmail popup notification.
3)Clicking any folder other than the current folder OR clicking send/receive BEFORE 60 seconds has passed forces the inbox/outbox folders to update and notification is received.

I have tested by sending mail to other employees using Outlook 2003 and this is what I've observed.
1)When sending to any user on the new server, mail notification for the recipient is delayed for up to 60 seconds.  If they click another folder or click send/receive they receive the message immediately eventhough my outbox continues to show unsent mail for about 60 seconds.
2)When sending to any user on the old server, mail notification for the recipient is instantaneous with no user interaction eventhough my outbox continues to indicate unsent mail for about 60 seconds.

From what I've seen I don't think that mail delivery is causing the problem because
1)users on the old server get messages sent from users on the new server immediately and
2)users on the new server can force the inbox folder to update and the notification to popup by clicking any folder other than the current folder

I'm thinking the issue has something to do with how Outlook 2003 updates its folder list when connected to Exchange 2007.

I know that complaining over a 1 minute delay in mail notification is somewhat rediculus but any help would be appreciated because I know that as I move more employees over this will become a bigger issue.

Thanks.