Test the Speed of a Local Area Network
Well you can just look at the network in the control panel and see if the LAN is connected at 10/100/1000 mbit. But that doesn't tell you the whole story. If you want to test the speed between two PCs, you really need a tool to do it. One tool I've used that seems pretty good is 'iperf', it's just a commandline EXE, doesn't require any install. 'ping' will tell you the latency, but not the available bandwidth.
Example usage of iperf:
On one PC run it in 'server' mode:
iperf -s
On another PC run it in 'client' mode, and give it the IP of the first PC: iperf -c 12.34.56.67
You may need to use larger packet sizes to get the full speed, try adding -l 64K -w 64K
or something.