Try with netsh:
C:\> netsh -c dhcp server scope 192.168.1.0 show clients
---
Shay Levy
Windows PowerShell MVP
http://blogs.microsoft.co.il/blogs/ScriptFanatic
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S> I have an application that I need to import all the MAC addresses for
S> all hostnames into. I haven't found a way other than to an nbtstat -a
S> COMPUTERNAME. Of course the only issue with that one is the machines
S> have to be powered on to get a result. Is there any way to extract
S> the MAC address from DHCP?
S>
S> Thank You,
S>
S> --GT--
S>