On Leopard you may use dtrace to add the functionality you're looking for:

DTrace Scripts | Collecting scripts and settings for DTrace-enabled developers

Top Ten DTrace (D) Scripts

(A nifty gui tool would be MenuMeters btw.)

To add a user on Leopard see a recent post & comments at OS X Daily !

A good general starting point to get Mac-related Unix information is OS X Links .

Cheers,

verno