Component video (the cable with the red/green/blue connectors) can be an HD output but is analogue so won't be as faithful a reproduction as you might want.
With output at 500 lines (pixels high) it sounds like you're using a composite video connection (the Red/White/Yellow connectors.) This is common on most consumer video capture devices and is limited to SD (and even then fairly poor quality). Therefore you're getting the best you can expect using that method. If you're in a PAL region you might get an extra 100 lines as NTSC is about 500 lines and PAL about 600.
What you need to do is get the software (from the Canon website) and connect the camera to the USB port of your machine where you can copy the contents off at the best quality.