I have pictures that I am putting on a website, but if I were to place them on the site, the page would take forever to load. How can I put a picture, thumbnail size on a page and once the mouse goes over the picture it pops-up full size?
gilray this method will also take time to load the image.
Try using compressed file format, gilray has given a good code example.
As you state the page loading speed getting down then you should not let user to give him an opportunity to see the big picture on mouse over, as it will still take time to load, it can also disturb your web layout as becomes large.
open the big image in a popup window, and use thumbnails in the page.