Movie dimensions keep changing!

Hi, I was trying to compress a movie using divx codec, I am using the program called virtual dub and the program keeps resizing my movies so they appear full screen on my tv. It is suppose to appear LTBX. So it stretches the image.

Anyone know a different program where i can control this or can help me?

also I am burning using nero 5

it always fills up my whole tv screen when i burn it, leaving the picture stretched