Outlook 97 and Windows 2000 Professional

We are using Outlook 97 for e-mail and have recently upgraded from an ISDN line to a fractional T-1. On our Windows 2000 computers we can send e-mail, but not receive. We also have Windows 95 and 98 computers and those machines can send and receive normally.

Another twist to the situation is that if I install Outlook Express on my computer (Windows 2000 computer) then I can send and receive with no problems!!

Do you have any suggestions for resolving this issue?

Thanks,
Mark