The router, if it has been used before, will probably have the old tennants ISP installed on it. This will be the username and password, plus the PPPoA of the ISP.
If it is, you will need to reset the router to factory settings, usually a secreted button on the router. The landlord may have already done this.
If you knew the make of the router, then you could find the address you need to access the settings of the router. The address is usually something like 192.168.2.1 or 192.168.0.1. This just lets you use the setup wizard of the router, where you input the user name and password of the prson with the internet account. Virgin should give you the two numbers you need for there account. ( PPPoA )
So you should hard wire the first computer to the network. Enter the address bar number and fill in the details. You should then get a green connection bar, in the router setup and you are then connected. The other computers can then just be connected to the network and they should connect straight away.
When all are connected, change the log-on password for the router, so no one else can alter the settings and put at least a hexidecimal passwor to secure the internet line. Write down the code you have thought up and put that on to every computer in the network. This will make the network secure.
If you can't find the access code for the router, ask the landlord for the router setup disk. This should walk you through the router setup.