It's been a long time since I've done any work on them, but from memory, I think Vue scales the image for you, Any format will do, that is, Tiff, Jpeg or PNG. Also just make the background white and the branches/ leaves black.

Good luck! and happy Vue-ing.

Adriaan Barel (a.k.a. Vege Mite)
"Morality, like art, means drawing a line someplace." -- Oscar Wilde