Shared IP address poblem

When one of the computers using my home network streams a film or links to a TV programme, my computer tells me I can"t connect because another computer is sharing my IP address. This does not happen when computers using my home network are just web surfing. Advice please.

How is your router set up for IP addresses? It should be DHCP, and each of your machines in the network should also use DHCP. That way the router keeps the IPs separate automatically. It sounds like one of your machine has a fixed IP that the router doesn't know not to issue and it's issuing it again under DHCP.

If you MUST have fixed IPs, make sure every machine and device in the network has a different IP number.

Thanks for this Jake. How do I check how the router is set up and make the necessary changes?

You'll need to read the user guide for the router. Nearly all routers use an internal web page for administration. That means you use a browser (like Safari) and type in the local IP address of router, and you get a web page with several other pages of setup menus.
You need the manual/guide to find the "default" admin username and password to login. Some ISPs (internet service providers) who provide the router put a sticker on the router with this info.

You can find the router IP address on your Mac, too. Look in System prefs > Network, and you'll find an IP address listed under "router," or "gateway."