Stop automatic login to email box in Groupwise 6.5.1 and Microsoft Netowrk

We have migrated our network from Netware to Microsoft 2003 server and therefore no longer use the netware client - since we don't log in to Netware servers.  However, we still maintain our Groupwise system on Netware servers - GW 6.5.1.  In a pure Netware environment, login credentials were passed to the Groupwise client and your email box was launched as long as they matched the credentials stored.  In our current environment, no credentials are being passed to the Groupwise client and it launches using the credentials of the last person who had been on the system - when the email box does not have a password; with a password a prompt appears that allows you to change the username and password.  As an example, user1 logs onto a workstation using their own windows domain credentials and opens groupwise - no password set and no password entered - and after reading all of the email closes Groupwise client and logs off of Windows XP.  Later, user2 logs onto same workstation using their own windows domain credentials and opens groupwise; however, the email box that opens is from User1.  I was never given the opportunity to supply username or password.  How do I make it so that the windows domain login credentials and the groupwise credentials must match in order to open the email box automatically or prompt user for username and password?