I know linux servers can easily be set to log information exactly like that on their own. Try asking the NT forum here for the procedure for doing so with it. Once the system is logging those things, it'll be a sinch to regexp out the users and times for html viewing or what suits your fancy. Sorry i'm not NT savvy, but i'm sure someone, somewhere is.
If there isn't an already set up system in place (which there really should be), you could create a perl script that runs everytime automatically when any user logs on that would append their username and the time to a file.
Hope this helps.
:-Q "If you think you're too small to make a difference, try spending a night in a closed tent with a mosquito."