Pause and resume download?

Okay guys, I have a gallery set up. I am using only main images and having them resized to thumbnails at run time. So it downloads a full size image and makes it into a thumb. When the user clicks on the thumb the image is in the cache already and therefore pops up instantaneously.

The problem comes in when a user clicks on a thumb at the same time while another image is downloading. Something happens and all they get in the place of the main image is just my imageholder. This only happens while the images are being downloaded, as when the final image is done downloading, it all works perfectly. Since the galleries will have 200+ images, I can’t just have the user wait until the download process is complete. I am not exactly sure what is causing this, but I figure if there is a way to interrupt the download when a user clicks a thumb, then resume when the thumb pops up, or have a thumb wait until a download is done until it pops up.

Not really sure, but I hope this all makes sense to you guys and I hope that there is somebody that can give me some advice. Thanks guys.