I have 2 pc's 1 upstaires the other down I wish to hook them up to my cable.

what do I need?

I dont want to go wireless as its expensive about £120 - £150 I know I'll need another ethernet card and cable will I need a router? and is that it and how much are they? not after the best one just something good but cheap

if one computer is always on then you could have the other computer going trough that one (one computer needs two NICs, and you need a crossover network cbale to go form computer to computer) or do it the easy way and get a wired router and make sure both comps have one NIC......

Wired router is easy.

I got one for $30 USD and it works fine.
You'll connect you cable modem to cable drop. then router to modem. Then have regular ethernet cables to the router from each computer.

If you running 2000 or XP use the ICS option.