How do you get other world terrains other than GEONOSIS? I'v tried tat1.tga and all I get is white!

Try putting other terrain files (from your Assests/Shipped Worlds) in your projects World1 folder, then use them in editor.
example: take the bes1 TGA, and what ever else you need (bump ets), out of C:\BFBuilder\Assets\Shipped Worlds\Bespin\World1 and put them in your project's world1 folder. Then Zeroeditor will understand what bes1.tga is when your project its open. (ALWAYS copy and paste, not cut and paste)
GOOD LUCk

I already fixed this thank you.