DTM has added a couple of planetary environment OPTs...
Naboo is a second release, with new textures, a new town, and a new sky...and playable at maximum resolution.
Hoth is a simple environment, but released in conjunction with the OPT are the re-done AT-AT and T-47 Airspeeder in the "Battle of Hoth" shipset from ATX.
Screenshots of the environments can be found in the release thread on the XWA Upgrade forums
. The environments are available for download at MTD Industries