I know it is an experimental test track but was wondering if anyone knew how one might be able to ride the Yamanashi maglev train on one of its test runs?
The Yamanashi Test Track has the experimental Maglev train. For fairly obvious reasons, they generally don't have passengers - although there's a practical section for it.
Currently it's about 18.4km long and will become part of the Chūō Shinkansen connecting Tokyo, Nagoya, and Osaka - but at present it's being extended to 42.8km to be finished by 2013/2014, at which point the 9 trillion Yen (!!!!) project to build the new fast Shinkansen will kick off (it got approved earlier this year).
Citizens of Yamanashi Prefecture and government officials in the area are eligible for free rides, and over 200,000 people have taken part thus far. The city has a population of around 860,000 - so that's quite an impressive number of the city.
HOWEVER, for paying customers (unless you're willing to settle in Yamanashi for a while and become a resident!) rides won't restart on the test track until they near completion of this current upgrade - likely on weekends and during the summer holiday time in 2013 or later (if it runs over schedule), according to this article.
So short answer, unless you move there or join the government, you're going to have to wait a couple of years. And now you've got me considering a trip to Japan in 2013 ;)