I'm not an expert, but I do know that if a data base is in the format of Access2003, those users will NOT be able to access the data if they are using access 2000. Access will tell you that when converting a data base from an older version of access to a newer one. Access 2003 has what is called a sandbox. The new code in Access 2003 recognizes code that was ok to use in A2000 as a possible virus, etc threat, especially the macros. Neat huh!
Also, my son, who IS a program engineering expert, stated that his company bought all the engineers new laptops with vista, NONE of their software worked with it! They had to wipe out the brand new hard drives and reinstall XP on them in order to continue to do their jobs!
Suggestion.... have you tried to eliminate the password login criteria to see if you can access the data? If you can, then there is a problem with the login function.
Also, are your computers equipped with 2gb of memory. Dell's website states that this is a minimum requirement in order for Vista to function without hangups.
So, my question, is a little different. I want to be sure that there aren't other quirks that are directly tied to the new operation system with access 2000.