I finally got Forestry properly working without BC (first time i derped, by forgetting to delete the IC²-API inside it), and after i tried, to insert a Refractorycapsule of Lava, into a Geogenerator, the game crashed, because the BC-Integrationpart wasn't loaded...
2012-08-27 10:58:55 [SEVERE] A critical error has occurred.
java.lang.NoSuchMethodError: buildcraft.api.BuildCraftAPI.getLiquidForFilledItem(Laan;)I
at ic2.bcIntegration31x.common.TileEntityGeoGeneratorBc31x.gainFuelSub(TileEntityGeoGeneratorBc31x.java:28)
at ic2.common.TileEntityGeoGenerator.gainFuel(TileEntityGeoGenerator.java:71)
at ic2.common.TileEntityBaseGenerator.n_(TileEntityBaseGenerator.java:118)
at xd.n(World.java:1971)
at net.minecraft.client.Minecraft.k(Minecraft.java:1871)
at net.minecraft.client.Minecraft.x(Minecraft.java:825)
at net.minecraft.client.Minecraft.run(Minecraft.java:753)
at java.lang.Thread.run(Unknown Source)
Edit: This happens everytime i insert any Item (I tried Oaklogs for example) in the Bottomslot of the Geothermal Generator! And it corrupts the World everytime! (Good for you, that i can decorrupt Worlds)