how to fix in a dishwasher and what do i need to buy?

Do you live in the UK or US?
If you're a yank then I can't help due to the language barrier.
How close is the dishwasher to the sink or water supply?
If it's adjacent to the sink it's relatively easy to do as there's less actual plumbing involved. Although anything is easy when you know how to do it.
Find out how many water hoses go into the machine, and do they link to hot, cold, or both? Look at the connector at the far end of the hose, red is hot, blue cold. Alternativley RTFM.
And find out if you have a plastic waste under your sink.
Post the answers and I'll see if I can help.

Big Softy
October 2008