Hmmm...cropping shouldn't do that. Are you maybe talking about resizing it?
Just as an example, I started out with this pic for my signature:
(Please don't download it too many times, I need the bandwidth for an eBay listing.
Anyway, I chopped portions of the top and bottom to reach a height of 100 pixels and chopped a little off the right side where you can see the middle of the magazine it was scanned from. Then, it basically became what I have in my sig. Sometimes you have to crop and resize to get to the desired size, but it shouldn't turn out fuzzy or anything (at least it doesn't in Photoshop). Can you maybe post or email an example to me (original and altered)?