Here's an inexpensive way to get your feet wet in Vintage Trials. With Unadilla, The World Round and Kentuck coming up soon, this would be a great bike to pick up and have fun, without having to pour money in to it. Looks like it just needs a rear tire. Put a wanted post up, and you could probably get a very usable one for free.
http://hartford.craigslist.org/mcy/5029351080.html
I don't know this bike. Just happened to see it on CL.