Draft for exporting from Blender 2.63:
Be sure to grab the updated exporters (2.63+), I've pushed them to the repository:
Drop them to <blender_dir>/<version>/scripts/addons/
Go to: File -> User Preferences -> Addons tab -> Import/Export Category, and enable the Quake2 MD2 and UFO:AI TAG exporters.
Open your model, assign it at least one texture, Important: The texture name will be the models skin name, UFO:AI uses as convention: ".texname" note the leading dot and the absence of file extension.
Select one and only one mesh, go to File -> Export -> Quake MD2, if you are exporting a static model uncheck the 'Export animation' checkbox, select filename and path, Save! (Note about animations: the exporter will export all frames from the current Start frame to the current End frame, set them appropriately or you may end with extra/missing frames)
If your model has tags, select all the tags you need to export (tags must be 'Empty' objects) go to File -> Export -> UFO:AI TAG, select filename and path and save, the tag file needs to have the same name as the md2 (Note: as above the exporter will export all frames from the current Start frame to the current End frame, they need to be the same number of frames than the md2 or the game will error out)