Big question. To get a better answer, I'd look through Access help and maybe read this:
http://support.microsoft.com/support.../q132/1/43.asp
But, yes, using Access (97 or 2000) workgroup administration, you can control which users have access (permission to see, edit, etc.), who can or cannot log in, and even what records are returned in a query. It can get very sophisticated.
From what I can judge of your familiarity with Access (judging from your other posts), I would warn you that you can get yourself into some sticky situations if you don't have a solid understanding of manipulation of security parameters. Keep in mind that adding security is often one of the last steps that a developer takes before rolling out a complete software package...
For what most people use access for, most of the time, security is more of a headache than a help. If there are confidentiality problems, you can usually get around them through your db's design (yes forms and reports are
much more than pretty faces), or using computer- or network-level security such as you suggest in W2k/NT.
Hope this helps.