I too have Blueyonder Broadband and have a very easy and simple network. No need for routers, switchers or other costly hardware (though if you run Win 95 or 98 things won't be so simple).
Heres how it works:
Main PC running XP home edition has USB connection to the Motorola SB4100 cable modem. This PC's network card connects to second PC's network card via 10 metres CAT5 cable and crossover plug which I bought from Maplins (a chain of electronics stores here in the UK).
Second PC runs Win 98SE (this version has networking capabilities that standard 98 doesn't have). I had to set up various protocols sutch as Netbui and others I can't remember on the client machine before the 2 PC's could 'see eachother'.
Next, I run a programme called 'Proksi' on the host machine. Its free from
http://www.networkingfiles.com/Proxy/Proksi.htm and allows the client PC to connect to the internet via the host PC. By the way, the host pc's Zonealarm protects both machines!
Don't forget to configure Zonealarm (or other firewall) to allow the client PC's network card's IP address to have permission to access the internet. Its a bit fiddly, but the sense of achievement when a luddite like me got the whole shooting match to work was great. And just for the record, I'm posting this message from the 'client' PC!