> As far as I know Drools Flow Eclipse editor works only in Eclipse 3.3.
 
This depends on the version of Drools you are using. For Drools 4.0.x you have the choice to use either Eclipse 3.3 or 3.4 (just select the right download), for Drools5 you'll have to use Eclipse 3.4.x.
 
> Also the RETE tree sometimes doesn't show.
 
There was an issue but this has already been solved on trunk (a few weeks ago), so it should work again in the next release.

Kris