1. You could upload it to
Webshots and use their sizer on the side. It has the option to post 100, 200, 425, 500, and 600 pixel sized images regardless of the file size. That will help, but it will not solve all of your problems
2. Download
Picasa which is a free editor program hosted through google. It will allow you to edit, resize, and organize all of your photos on your computer. You can also effortlessly send them to an online storage site through google and have them ready whenever you need them.
3. If you have a copy of Photoshop, you can tell it to resize your photos to any given size needed. For starters, I'd recommend Photoshop Elements 5.0 or 6.0. Usually you can find this around $50-$70 if you catch it on sale.
Hope any of those will help you with your resizing. Ask away if you have any more questions.