AD Network questions re unknown machine names on our lan

I am running a small office network - about 60 machines on a Win 2003 Server
AD Domain.
Most of the machines are wireless clients but some are hardwired into Lan
Switches. All are WinXP/Vista clients
Upon inspecting the address leases in DHCP on the server machine I note that
there are a couple of machine names which are not familiar to me and I
suspect that they could be outside machines logging in - somehow gaining the
wpa key .
Can I somehow discover whose machines these apparent rogue machines are by
sending a net message in some way ?
Can I block them by mac address and if so how ?

While I have been considering this problem, I have just noticed that I
appear to have 2 DHCP servers on the network. One running on the Domain
Server and another running on the ADSL / Modem/ Router which we provides
internet to the LAN. Both are in the same range.
This seems on the face of it quite wrong - is it ?
I have occasional restarts of routers but nothing exceptional and we've been
running like this for 6 months or more.

1. Two DHCP servers may cause a problem. It is better to keep windows DHCP
only.
2. machine names: Do you use VPN? if yes, the remote computers may register
their hostname. Or perhaps your employees bring their laptops?
3. You can use WPA and Mac address for wireless access. Be care that they
may cause wireless connection problem.

--
Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on
http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on
http://www.HowToNetworking.com
"-keevill-" <(E-Mail Removed)> wrote in message
news:O2$p8gQ$(E-Mail Removed)...
>I am running a small office network - about 60 machines on a Win 2003
>Server AD Domain.
> Most of the machines are wireless clients but some are hardwired into Lan
> Switches. All are WinXP/Vista clients
> Upon inspecting the address leases in DHCP on the server machine I note
> that there are a couple of machine names which are not familiar to me and
> I suspect that they could be outside machines logging in - somehow gaining
> the wpa key .
> Can I somehow discover whose machines these apparent rogue machines are by
> sending a net message in some way ?
> Can I block them by mac address and if so how ?
>
> While I have been considering this problem, I have just noticed that I
> appear to have 2 DHCP servers on the network. One running on the Domain
> Server and another running on the ADSL / Modem/ Router which we provides
> internet to the LAN. Both are in the same range.
> This seems on the face of it quite wrong - is it ?
> I have occasional restarts of routers but nothing exceptional and we've
> been running like this for 6 months or more.
>
>