It was posted/LAST UPDATED 07 November 2010, a YEAR ago. It was made for the old Indev save system for maps, a system no longer used. So it can NOT read your map data anymore to generate the forest. This has been abandoned sad to say.
There maybe now people will see it.
Incorrect. The fact that the world format this program was created for is no longer in use does not mean that it is entirely useless. You can still generate worlds using this tool and play them in the current version of Minecraft.
Step 1. Downgrade to any version of Minecraft before Beta 1.3 with Minecraft Version Changer or MCNostalgia and use it to generate a world.
Step 2. Use this program on the Alpha or Beta world you just generated.
Step 3. Upgrade to any version of Minecraft between Beta 1.3 and Release 1.1. Load the forest world you just created and convert it to MCRegion format. After the world is loaded, quit.
Step 4. Upgrade to the current version of Minecraft. Load the world you just loaded in B1.3-1.1 in the current version and convert it to Anvil format. The world is now playable in the current version of Minecraft. Enjoy!