I would have jumped in here last night to help, but I spent the evening in a walk-in clinic and then conked out...nothing serious, just very umcomfortable...a viral infection.
Now that I've excused myself, I will mention as I have in other threads that Paint Shop Pro is absolutely wonderful and is under $100 and has nearly the power of Adobe Photoshop. You can find it on this page in my bookstore:
http://portraitartist.com/bookstore/software.htm
In PSP, if you just hold your mouse over the image and in the lower right corner of your PSP screen, it shows the size in pixels. Then, you just do as Mike mentioned...edit, resize and you can then select the number of pixels you want your new image to be. If you want to keep the original larger file, choose "file save as", which allows you to create a totally new file with a a new name.
When you do the "file save as", there is an option button that appears (be sure to select .jpg as your file type before you click options) that allows you to select the level of compression. Select higher quality compression; maybe around 15.