Dear Chirstian,
Hope you are trying anyone of this below commands from isql
1> select * from master..sysusers
2>go
1>sp_helpuser <User_Name>
2>go
1>sp_displaylogin
2>go
1>select * from master..syslogin
2>go
Hope any of those will solve your purpose.
PS: sp_displaylogin has a parameter called - "Default Database" which says the DB assignment details.
Regards
Kiran K Adharapuram