when you drop the video onto the video track in vegas there right click the video and select properties
then uncheck maintain aspect ratio
there are videos on youtube explaining how to do this
[ame=
https://www.youtube.com/watch?v=gGtjLO6pq00]YouTube - How to remove black bars in HD Videos (Vegas Pro)[/ame]
or to get rid of the bars at top and bottom if that doesnt work
drop the video into the video track and then click the middile symbol on the track its like a screen or somethin

then you have remove the ratio things in that page, then just change the size of the image
simples

if that made any sense
basically what ngu said but talking you through it.
hope it helps
Pikey