OK, I finally got the cog/lockring situation worked out. It took so long because of an unexplained disaster with my brake (it came to my attention while I was riding through downtown, thinking to myself how I probably shouldn't be riding with an unsecured lockring, immediately followed by some impatient joker turned left across my path and me squeezing the lever which promptly did almost nothing) and a blowout the next morning (oops, no rim strip - luckily it happened while replacing the brake).

After I got off work today, I rode uphill, applying as little backward pressure as possible, for about four miles to the LBS. There, I tightened the lockring until it would go no more. Put on a rim strip, paid my fifty cents, and went to the street to practice. A few three inch skids later meant success.

Many thanks to all who chimed in with their thoughts.