kosmo vinyl:
Go to mapquest and simply put in Rockville, MD for start and Columbia, MD for finsih. It should give you directions using 28E (NORBECK RD.), 198E and 29N. This basic way can be crowded but has saved me a lot of time in the past.
If it does not work on the first try in mapquest try again and chose avoid highways but it should work if you simply start at rockville, MD and end columbia, MD (no actual street addresses)
Jason