How to track which users logged in to sql server

use
   select * from sys.sysprocesses

it will list all process and what users are connected

Thanks for the comments, will this give information only for the users who r currently logged in or also for  currently logged off of or users no longer in that session( disconnected)?
I mean in case if I want to find out which user logged in in last 30 min or so and they might have closed their session by the time I am executing this cmd

I would use SQL Profiler and build traces that would track audit login and logoff events.

There is a great topic on this at http://msdn.microsoft.com/en-us/library/aa905160(SQL.80).aspx

Thanks