I've basically just done exactly this. I added a Network Switch to my single LAN port on my Router and then added all the other PC's etc to the Network Switch. It's completely transparent and you don't need to change anything. But do use a Switch rather than a Hub - they are almost the same price. A Switch directs specific data to specific devices whereas an Hub broadcasts the data to all devices and can cause congestion on a busy Network.
I bough this 8 port switch for £7.99+VAT+P&P click here