is there any program/server plugin/etc that can be used to generate, say a forest, around a building i created? however, it should not delete any of the blocks of the building. i want to make it look old, like the forest overran the place.
WorldEdit's forestgen (both available as bukkit plugin for SMP and as SSP mod) can generate forests centred around you, but I don't know whether this will skip your house (I think it won't delete anything but you might end up with trees on your house, I never tried this). You'll probably have to chose at least four places a bit away from your house and generate smaller forests that don't reach your home.
Alternatively, plant some saplings manually and use bone meal to immediately grow the trees.