One quick and easy way to resize your pictures is one I use and you can run a "batch" of them at once for future use. I have Windows XP and use Outlook Express so it may not work on other systems.
#1 choose the files you want to upload, you can prepare several for future uploads (batch method)
#2 After choosing the files, right click on the last one and use the "send to" - "mail recipient" option
#3 A pop-up widow will appear asking if you want to resize your images, you get several options, so try them by trial and error, the smallest one fits a 640 X 480 window
#4 Send the message to yourself then open Outlook Express and look in the outbox, your message with the images files should be there
#5 you can then save the files to a folder, I use the folder names small, med, snd large. Then after that you can delete the email message. I can get all my files under 100 KB with the smallest setting and it will resize most of them at the medium setting (800 X 600) to under 100 KB too
No extra software or hoops to jump are required in this method, although being in computers for 35 + years I have so much software I have developed and accumulated, I myself can do it several didderent ways, I also have a great thumbnail generator program that was in the free domain. If my instructions are not clear I guess I can make a video if it is need