Hi there

Most routers allow you to start DHCP from a specific address so you can have a number of static ones on your LAN.

I have some static IP addresses for special hardware - controllers for a Logitech squeezebox system - the clients for a Media server. These have their own embedded Linux OS in them and if these are restarted using normal DHCP they can reserve an IP address that a normal PC is using - and these devices don't detect that a Windows machine is already using this so they can't logon to the media server.

Another perfectly valid reason you might want a static address on your computer (LAN static address) is that you might want to access the machine from a remote location via RDP. RDP requires the command to be routed to a specific port on a specific machine. Your router should have a Port forwarding option in the setup.

I don't think the OP has got any ulterior motives like bypassing Virgin Media's site blocks -- that's done totally differently. Assigning some static IP's on a LAN is perfectly normal.