the images are too large,
exactly how large, file wise? what are the actual image dimensions? what are the display dimensions? are you scaling down the image for display?
What is the image file type?
You will need to strike a balance between what you deem as "quality", file size, and acceptable download time... a download time which could vary greatly between users.
As for the other post you mentioned... are you wondering about how to create a "preloader"?
Here is some basic details