is out here any mod to add some vehicles to the game? the TIE Defender for the Imperials, as an example

I'm not sure about adding vehicles to the game, but i've definitely seen custom made maps with new vehicles, Coruscant City for example has speeders like on AOTC, and an Utapau map that I saw had the walker from Clone Wars on the PS2.
http://starwarsbattlefront.filefront.com/)

EDIT: http://www.pcgamemods.com/9.html) PCGamemods has vehicle mods for Battlefront I but not Battlefront II.

and they can't be converted?

youd need the person who made the vehicles to re-export them cause the directories are different and youd have to redo the .odf file cause of all the things they added to the flight part of the engine. its very possible, ive made tons of vehicle models and units.