Yes, you can swap those rings for a 50-34 setup. You might also want to consider a 12-27 cassette. A 36-27 combination is slightly lower than 34-25 would be, and obviously 34-27 is lower still. FWIW, an 11-27 cassette (not as common, but available) would give you almost the same gear range with your current chainrings as a 12-25 would with 50-34 rings, so that's probably the cheaper way to go as a first step.

See also: http://www.sheldonbrown.com/gears/