expansion/header tank query

[Speedy Gonzales]

Please forgive my ignorance but what is the difference between an expansion tank and a header tank. I only ask as at the moment I have a rather discoloured horrible plastic rover V8 expansion tank which I would like to replace with a nice shiny aluminium or stainless steel one. Ive seen a expansion tank kit for sale by ratsport for £74.95 which includes everything from hose clips to the tank itself. However, my current expansion tank simply has a cap on the top and one hose at the bottom which enters the top of the radiator. The expansion tank that ratsport have for sale has the oulet at the bottom but there are three others on the top. The only spare hose that I have if you like is the overflow pipe from the top of radiator, so what are the other two for or is this expansion tank no good for my set up and I simply need to find one which has a outlet at the bottom and a inlet at the top for the radiator overflow.