This has been discussed many times and at length on the forum. The short answer is that everytime you save as JPEG there is some quality loss. The ammount varies by compression levels and if you resave after editing. Whether it is discernable to you is another question.
If you have a 10D, my preference would be to shoot in RAW and archive the unedited RAW images. Then if I save copies after editing it doesn't really matter what format I choose, because I can always go back to the Raw source file.
If space is a problem, look into investing in a second hard drive. They are cheap these days and big.