If you are using Windows of any kind, you have the perfect (and easiest) program available to you for resizing pics already installed:
Paint
Yes, that wonderful little program has a feature in the drop-down menu under "Image" called Stretch/Skew.
Load up your image in Paint, hit "Image" then go to "Attributes". It will tell you the image size in pixels. Figure out a percentage of these numbers to get you to 640X480.
Then use the "Image" > "Stretch/Skew" to shrink the image by the above found percentage.
If your image is already 640X480, but is some exorbitant file size, just load the image in Paint, then resave it under a different name. The JPEG compression will reduce the file size each time you re-save it as a different image (hence the renaming).
Hope this helps some who are itching to post pics, but don't want to wait all night for the 4MB file to upload over dial-up!!