It sounds like either the door seal or the tub seal has gone, Both are easy to replace, but you have to make sure of the following,
Door seal has to be in the correct position
Tub seal is a bit more involved as the front has to come off, Make sure that the lip & edge is spotless from scale, soap etc. I would recomend that you consult the Haynes washing machine manual if you get really stuck.
Rob
May 2006