You can get it here::
IP Addresses for Mechwarrior 4 Mercenaries multiplayer servers
You can also simply connect via an IP address.  There are many dedicated servers for Mechwarrior 4 Mercenaries.  Within the game, click on Multiplayer.  On the next page, under select a connection, click on Edit.  Under Connection Setup how would you like to browse for games, click server name or IP address.  You can only enter up to 5 addresses.  So you will have to make more than one connection.  Make sure you don't have any spaces between the IP addresses, and separate them by commas.
Having problems finding multiplayer games for Mechwarrior 4?
You can view servers and their IP addresses by going to one page.  Just hover the cursor over the server name and its IP address will appear.  The site is:
When you double click the icon the following dialog boxes appear.  Just click Yes.
www.mektek.net/mekmatch
July 28, 2009 - Mechwarrior 4 Mercenaries (including Vengeance/Black Knight)
no longer has multiplayer support through MSN Zone or Zonematch.

GOOD NEWS!!  Mektek, a software development company, has
created a new multiplayer zone.  All you have to do is download
a small file and it will redirect where the game looks for its multiplayer
server.


The only change is a registry entry:

[HKEY_CURRENT_USER\Software\Microsoft\Microsoft Games\Mechwarrior Mercenaries]"Zoneserver"="mwmatch.zone.com"                

to

[HKEY_CURRENT_USER\Software\Microsoft\Microsoft Games\Mechwarrior Mercenaries]"Zoneserver"="mekmatch.mektek.net"

You can make the change yourself (run Regedit from Start Menu and select Run) or double-click the
mekmatch registry entry already in your Mechwarrior Mercenaries main folder (if you have downloaded and installed all the Mektek Mekpacks up to 3.02b - visit www.mektek.net/projects/mp3 to get these patches).  This is the preferred method.  Note, If you have not patched your game to 3.02b through Mektek, you will see servers but not be able to connect.  You will see the servers green which means they are a different version.  Also, make sure ports 2300-2400 are open on router/firewall.
Download Now
Update:  It is now called mekmatch.reg and not test-zmserver.reg
www.mektek.net/projects/mp3
Get my maps at www.randymgames.com/mw4maps