Kooshmeister,
I don't think that the pixelation (or whatever) has anything to do with the XnView resizing/compression step, so you might as well go ahead and get back into the habit of resizing before uploading to imageshack for future contributions. It would save time for the admin who uploads the images (especially if there are many cars like this one, and/or if imageshack is being less than cooperative).
Thanks.