Problem burning dvds with subtitles in Win Vista

Hello everyone,

Seeing I’m a total newbie concerning creation and burning dvd images, I couldn’t find a free program that could convert an .avi film to .iso format including .srt subs.
I plan to burn the image with Nero 7.

I’ve already try loads of programs but they just don’t work with Vista.
Please, could anybody tell me which is this magic free program that convert avi to iso with subs when we use Windows Vista?.

Thanks a lot!!!