Virgin will allocate your "internet" IP address automatically. If your computer connects directly to Virgin via a Modem (Cable or ADSL), it will get this address.
If you use a Router, the Router will get the address allocated by Virgin automatically. It [the Router] will then allocate LAN IP addresses to any computers connected to it, using one of the address ranges reserved for Local Area Networks, most commonly 192.168.x.x addresses. If you have a particular need to allocate fixed IP addresses in a Local Area Network, each computer must have a unique IP address in the *SAME* Subnet (IP address range) as the Router.
Therefore, if your Router's IP address is 192.168.1.1 then any fixed IP addresses you use must be in the range 192.168.1.2 to 192.168.1.254 with the Subnet Mask address of 255.255.255.0 and the Default Gateway address which is the Router's IP address (192.168.1.1). You will also need to allocate the DNS Server addresses, one of which can be the Router's IP address.
If you are not familiar with IP addressing, I'd suggest you stick with getting all of the addresses automatically.