Not just cropping, the camera shoots at 72 DPI with a size of 2560 pixels by y pixels, (pg 150 of PDF) so for Web 640 x 480 is way big enough, can even go smaller, so just resizing to that is going to make a difference, also ou can changee the compression - the higher the compression the greater loss of quality, but then again for the web, not as critical.

So if you crop the picture then resize then recompress you should be in good shape for web (BUT not for print)

CRITICAL POINT - make copies of the orginal pix from the camera to work on and do not work on the originals - in fact it is a good idea to back up the originasl also to hard drive and/or CD-R/DVD (which are also inexpensive nowadays)