inventory of workgroups

I need to find a way to audit\inventory all computers on a network, acquiring Operating System, IP, computer type (example: HP, MAC, DELL, etc.) nothing else really matters.  These are the criteria’s:

1.      Some computers are linux\mac\pc
2.      Some computers are on a domain
3.      Some computers are a standalone machine in its own workgroup
4.      Not all machines have the same password (but I know all of them)
5.      Not all machines have the same administrator username (but I know all of them)
6.      I cannot have physical interaction to “all” machines
7.      I can and have pulled all IP\MAC addresses\VLAN  (but cannot tell what Operating system or type of machine)

Any ideas? I have tried other third party software (10-strike,IDEAL,Spiceworks), but for these, the issue is with password ( I cannot distinguish what machine has what password).  Eternally grateful