I have PS Elements 5.0 so it might be different, but here is how I do it: In edit mode, with your photo open, go to File, then "Save for the Web" and then adjust your size so the longest side is no longer than 800 pixels. Make sure that it constrains the proportions. Then, adjust the "quality" by using the slider scale. While you are doing this, look at the adjusted photo and along the bottom it will tell you how many kbps it is -- you need it below 100. Then hit "apply" and save it (use a different file name as you don't want to replace your original). Next go to a photo hosting site, like photobucket, and upload your photo. It will give you three links under the photo once it's uploaded -- use the last one and paste it in your post to display your picture at the size you uploaded it.
Hope that helps.