You don't really need to replace all the hoses. They are VERY expensive. Just remove them and flush it thoroughly. You can buy A/C flush in cans that work great. I'd rather buy a couple more bottles of the flush than replace those hoses. IIRC they are well over $100-$150 for each line.
Give a good read of my Evaporator page....Plenty of links with all the information should ever need:
http://w124-zone.com/?p=93