Ryan Brill has a good article on creating a nice Form Highlighting effect with Javascript. This is very similar to the recent A List Apart artilce: Creating Custom Corners & Borders. Only this has no height constraint. You can see Andy's sample here on his site to see it in action.
I do like how he avoided fighting with the DOM over the differences on how IE and Moz generate child nodes. He puts the code on one line. Ugly in the source, but it works. (If there are spaces between elements, Gecko broswers assign a child node, while IE does not.)
Nice effect. Nice tutorial.