Also, set a static internal IP. This is a setting in the router admin control.
There may be a setting in the router than needs to be changed, but most of the settings for this are on the individual computers.
I don't understand the bold.
'ip stuff' im guessing is referring to setting a static IP
'extending ip range' you should only need to do if your router has some sort of ip filtering enabled. Check any filtering settings you have enabled just in case.
Second number should be 280--
replace the '--' with however many people you want to be able to join your server.
The two boxes for port number are for inbound and private port, not start and end of a port range, so no. According to the link Isjix posted, he needs a seperate entry for each port, with the inbound and private port the same for each individual entry.