Basically what I am asking is, is there a way to have say a 1000x1000 pixel image and simply have some sort of code, whether html, css, or anything else to only download a resized verison of 100x100 pixels. Is there any way to do this? I would like to know before resizing each of my pictures and uploading them and linking those photos to the original larger version. Thanks.
You can't do it with HTML/CSS but it is possible with a server side language like PHP. Here's a script that will allow you to resize images.
The catch is that resizing images can be a server intensive process. You should try to make sure that once you've created a resized version of an image, it's cached on the server for subsequent requests.
Along those lines, the flow should be:
Note: James brought up a good point in the comments. If the images you're resizing are going to change (updated/edited), you'll need to keep track of their large image's last modified date when you create the thumbnail (as part of the filename or in a database).
That way, when you check the cache, you'll be able to tell if the thumbnail needs to be regenerated.