What sized sprocket did you want to run on the rear? I think the largest rear gear you can get for the rear is 21 tooth. Do not know if that would give you enough gearing if you go with a 42t front chainring. Otherwise, you are going to have to find a crank with at least a 130 bcd to use a 38t chainring.

http://www.sheldonbrown.com/harris/chainrings.html

Tom