Higher res. with ffmpeg problem

Hi,

I have:
Logitech QuickCam Pro for Notebooks
HD video 960x720

Using:
ffmpeg -f video4linux2 -s 640x480 -r 24 -i /dev/video0 -f oss -ac 2 -i /dev/audio1 test.mpg

to capture. What do I have to do to get higher res.? The output is lousy with the above ffmpeg commands.

Thanks,
Jack