If you want to resize or reduce the size of your image files in order to upload to this site, irfanview is the best freeware image tool I have found - images load instantly, and all I do is save the image to 75% quality which makes the file size significantly smaller.
However, for my own pics, that is way too much trouble. I take my pics at 10 mp resolution and upload them directly to Picasa web albums - they are full size, but I limit to a maximum of 2048x2048 pixels because that way Google will allow me to store unlimited numbers of photos. Picasa will resize on the fly. You can use Photobucket or any hosting site.
When I want a pic to display in a certain size in a post, I just capture the share url in Picasa, and change the forum's image tag (second row of buttons, first button on the left) to read whatever I want the image width to be. For example this is how the first part of the image tag looks like when the button is clicked:
[img] - this will display the image at full size
Now, if you want to change the size on the fly simply type in the width parameter like this:
[img width=400] will display a thumbnail 400 pixels wide - if a member is interested in seeing the picture larger, just click on it and it jumps to full size - click it again, and it returns to the thumbnail
[img width=200] will display at 200 pixels wide, and so on