client 6.0 upgrade

In the earlier ver. of remote desktop our users had to enter there user and
password, with the update the new remote desk top client keeps the last logon
user and server exp. sever1/user1 My Question is,
Is there anyway to prevent the server and user name from showing up in the
user name box, we have an windows domain and windows xp pro.
I've tried the settings in group policy and they did not work .
Before the upgrade our users had to enter both because os security reasons,
after the client upgrade they need to clear the user and then logon
anyway if anyone has any ideas it would Appreciated.