I use photo impact 10 for screenies.
I've found the following to be the most effective methods.
Firstly go to file - browse find and open your shot.

Then select adjust - resize and reduce to 800 X 600 making sure to keep aspect ratio ticked.

Next go to File - Save for web - entire image.

You are presented with two images, the left one is the shot as is, the right as it will be.
Move the quality sliders around until you get nearest to 100k and then name the shot and press OK

your shot is ready for upload.

Thanks, I use PI 11, very useful tip.