EXTRACTING A DATABASE USER'S LOGIN NAME THATS NOT STORED IN THE SYSLOGIN TABLE

I'M WRITING SCRIPTS FOR HANDLING A DOMAIN ACCOUNT CHANGE OVER. DID YOU KNOW WHEN YOU ENTER A NEW DATABASE USER AND GIVE IT A DOMAIN ACCOUNT LOGIN NAME, THAT DOES NOT EXIST IN THE INSTANCE\SECURITY\USERS LIST, THAT IT DOES NOT REGISTER IT IN THE SYSLOGIN TABLE? SO IF YOU NEED TO PULL THAT LOGIN NAME, YOU CAN USE SUSER_SNAME() BY
PASSING THE .SYS.SYSUSER.SID VALUE FOR THE DATABASE USER ACCOUNT IN QUESTION. I ORIGINALLY THOUGHT I WAS GOING TO HAVE TO ACCESS ACTIVE DIRECTORY DATA THROUGH A SMALL VB APP. THE AD ADMIN GROUP WILL SURELY NOT GIVE THAT ACCESS TO ANYBODY AND CAN FORESEE LOTS OF POLITICS AND PAPERWORK INVOLVED IN EVEN A FAIR SIZED ORG OF SAY A FEW HUNDRED PEOPLE! HOPE THIS SAVES YOU ALL SOME TIME!