http://www.renderosity.com/mod/tutorial/index.php?tutorial_id=1570&page=1

Try the above tutorial. It's an adaption of the technique that I use in Paint Shop Pro.

Personally Paint Shop Pro does a better job in this department because you can actually control the amount of compression to a larger degree. If you do happen to have Paint Shop Pro, here is my method of saving and / or resizing images without losing image quality:

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2678201

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi