I can only think of three things here, but none are perfect:
1. There is a way to tell a browser to only load PART of an image using an image map like structure. Basicall say your image is 100X100 pixels, you can tell it to load the first 25X25.
2. You can specify how big you want an image to appear, this would let you put many small pictures on a single page, but they would still take just as long to load.
3. You can tell graphics to load interlaced, where basically the first row of pixels is visible, the second is not, the third is, etc. This is a REALLY old switch, you'll have to search online in outdated HTML guides or go to your local library and check out a book thats back in the days of like HTML 3 or 2. They MAY have discontinued this switch because so many people have broadband now, but I don't know for sure.