It could be because of PNGs. Although the quality is better, the file size is much larger. So, it will take a little bit longer to load. Especially, if it isn't optimized for web.
You can use: Web Graphics Optimizer
. It's a free download and you can save as PNG and optimize the image as well, so that should
help with the loading problem.
Let me know if this helps.
"I would feel more optimistic about a bright future for man if he spent less time proving
that he can outwit Nature and more time tasting her sweetness and respecting her seniority."
E. B. White (1899 - 1985)