NOTE: This is outdated information that applies only to Tapestry 4. As of Idea IntelliJ 10, Tapestry is supported out of the box.
Tapestry source code already includes the necessary configuration to open it as an Eclipse project. If you're used to another IDE, let's say, IDEA, you're on your own.
... until now. Attached to this page are all necessary files to use Tapestry 4.0 eta-3 source code as an IDEA project. Just unzip the file over the tapestry-4.0-beta-3 source code, and open the "tapestry.ipr" project. For everything to work out-of-the-box, you just need to have two JDK's defined in your IDEA installation, named "JDK 1.4" and "JDK 1.5". You can always change this to something else later, if you don't want to use the default names.
Worth noting also that Idea 5.0 can now import Eclipse project file descriptions. No idea how that works in practice but the feature is there.