pal -> ntsc conversion?

[FirstBorg]

Hi
How can I convert pal to ntsc with virtual dub?
The original avi has a resolution of 640x360 at 25fps
I managed to succesfully change the framerate, but if I change the reslution to 720x480, which I need for an ntsc DVD, the aspect ratio is not the same.
thx

[scharfis_brain]

if you set your mpeg encoder to 16:9 (anamorphic), the AR will be okay

[FirstBorg]

You mean, that it does not matter if the AR is incorrect after the Xvid conversion, and this will be corrected in the later mpg encoding?