wow, weird pic!  

guessing your monitor is mounted horizontially?
are you running one of AVGA's special horizontal resolutions for vertical games?  e.g. 352 x 288 for galaga?  As this is not a true 60Hz mode, this may be causing the display issue with your monitor!?!?!
Anyway, for vertically games on horizontally mounted monitors, you may want to try the following.
- Enforce the res to 640x480
- Enable Hardware stretching
- Disable/Enable Bilinier filtering.  Test what looks better for the game/screen.
- Set the aspect ratio to make the original games res.  e.g. for galaga 288:224
- The effect RGB sharp may also make a difference??? but not that I can tell.
This picture will be interlaced, but its still looks acceptable on my nanao arcade monitor.