Downgrade?

I am new to Drupal and installed version 6 and really like what it does. Unfortunately, through experimentation I have found that several of my needs are supported in the 5.x version and not in the 6.x version.

Is it possible to install the 5.x version and then migrate my database over to it somehow? I have done a lot of work and really would prefer that I can move my data somehow instead of starting over with the over 300 nodes of data that I have now.