I dry seedless grapes all the time to make my own super delicious raisins (big, juicy, yummy) and all you have to do is "craze" them (make microscopic cracks in the skin by plunging them in boiling water for 30 seconds).
Cranberries are sour so they need a sweetening treatment before drying. My handbook had nothing so I looked it up for you and found a couple of links to instructions.
http://www.cranberries.org/cranberri...pes_dried.html
http://www.ehow.com/how_4898803_make...ehydrator.html
http://lowcarbdiets.about.com/od/snacks/r/driedcran.htm
Good luck!