There's not a lot of changes. Some things are now handled differently (like lists with images) so there's yet more browser-scripting, like dynamically changing styles.

Links

MSIE5 now supports a:active. For example when you have two frames, and you set the active style to text-decoration: underline, then click on a link in the navigation frame, then focus on the second contentual frame, the underline will not longer be lost like in IE4. Also, when you click on a link on one page which changes the page to another one, then you go back, the link is still active.
If you go to another part of the same page and then for example hit the back button, the link won't be active.

Minor changes

Overflow

Also the handling of overflow: auto for certain elements (like a textarea) works now.

Width

Some other change is that certain widths don't seem to be the same and take up additional space. This causes for example elements which floated side by side in a limited context (like a div with a certain width) to be now underneath each other. Once you know what causes this it's easy to change by adjusting the width of either context or nested elements.

Continue with: JS.