Just thought I would put the word out that Sketchup exports obj files that open and render perfectly, so if you have a version of sketch up that exports obj, or one with the plugin, you can make use of all your sketch up creations easily. There are also alot of trees/ plants available via the pro forum in skp format which can be converted to obj. Just make sure you get the 3d ones, as some are 2.5d.
The files once converted are pretty big though, the one used in these renders is 3 meg.
SeerBlue
yep, I've got Sketchup 6 (or 5, not sure) and the obj exporter works great, as long as the models themselves are good to start with