Tell all of your friends on AIM or MSN messenger to help you out by posting a couple things.
Get a real domain. No real members will ever join a free hosted site.
Have lots of general disscussion topics....
It is hard to start of with... It is like a mountain.
It is hard work to start off with but when you reach a certain point (the top of the mountain) it is alot easier and almost promotes itself (which is like walking down the mountain as it is easier the walking up it).
Im in the same position as you, but like other people have said: Post exchanges work well and once your board looks very active people will join almost automatically. Promote your forum anywhere you can.