The networking is still a WIP and is a little convoluted to setup.
Here are the steps I used to link two instances of Rush the Rock on one windows computer
1) Install openvpn link (https://openvpn.net/community-downloads/
2) Browse to C:\Program Files\TAP-Windows\bin
3) Right click on addtap.bat and select run as administrator
4) Right click on addtap.bat and select run as administrator
5) Go to Control Panel\Network and Internet\Network Connections
6) Right click on the adapter "TAP-Windows Adapter V9 #2" and select rename. Name to mame-tap1
7) Right click on the adapter "TAP-Windows Adapter V9 #3" and select rename. Name to mame-tap2
Select both mame-tap1 and mame-tap2 and right click and select bridge connections. I get an error message here.
9) Right click on the ethernet bridge and select properties. Make sure mame-tap1 and mame-tap2 have checkboxes selected in the top window
10) Start sfrushrk in the first directory and then exit mame after the rush the rock splash screen appears.
11) Start sfrushrk in the second directory and then change the serial number in the dip switches to something other than 6.
12) For the second sfrushrk enter service mode and change the car color from red to something else. Exit mame.
13) Edit sfrushrk.cfg in the first directory. In the network area change so that interface="1" .
14) Edit sfrushrk.cfg in the second directory. In the network area change so that interface="2" .
15) Start the two instances of mame sfrushrk in the two separate directories.
In order to network over one lan you would need to bridge the mame tap adapter to your ethernet card.