Simple Messaging in Win 2000

First off let me say I am new to the group and VERY new to W2K. I have a small dentist office that has 6 win 98 machines and one W2K. The Dr. had been used to using WinPop to send messages back and forth to his staff. The problem lies in that the W2K machine can recieve the messages but is unable to reply or to generate a new message. Any help will be great.

TIA
Brent