DOM KungFu

Lately I've bee stretching more and more my js skills in order to to all sorts of ahmm, Ajax stuff. I started doing it the old way IE Mac and old NS browser compat. That until I realized that my brain can't handle it and that browser compatibility is way easier to achieve if you ignore that 1% of the surfers that forgot to update and focus on those Modern Browsers.
So once I got pass that glitch I got myself the Prototype JavaScript Framework.
And it rocks.
Things like $, $A, bind, PeriodicalExecuter, Ajax.Request, Event.observe, Position.clone are cool indeed and they solve much of the js quirks you have to figure out on your own. You don't even have to grip on what's going on under the hood to get the job done. Eventually you will tough.
A good start would be the "Developer Notes for prototype.js" article written by Sergio Pereira.
Another good js library would be the "Yahoo! User Interface Library" that was released as OS a short while ago. This one solves more precise ui building problems as it offers some ready made widgets.
These two don't follow the same guidelines but you can use them together without problems.