Finding sharepoint fields using javascript

[Update: Removed custom javascript] I am clearing the contents of this post, as it still attracts a fair amount of traffic and I don't consider it to be a best practice anymore. I recommend you use a common library such as jQuery to do any sort of javascript sharepoint field manipulation. Examples of using jQuery with sharepoint can be found at Jan Tielen's site, and there is also a jQuery/Sharepoint field manipulation feature available on Codeplex.