I just stumbled upon this. For months I've been wondering why it is that the nature of web browsers is such that if you're building a RIA where text selection would be inappropriate, such as in client-side "widgets" and "controls" where text appears as a label or text over an image to appear as a button, etc, but is rendered using HTML just the same, you cannot disable the user's ability to click-and-drag and thereby highlight text, creating a selection. This was partly disappointing for security reasons--disabling selection makes it more difficult to copy things that shouldn't be copied--and it was partly for UIX (user interface / experience) reasons--hiding from the user the obviousness that this is just a bunch of DHTML tricks and not a natively running app. I've always figured it was not possible in HTML to disable the user's ability to select text on the document. 

I was wrong! There's an old hat trick that's been around for quite a while. It's documented here:

http://support.microsoft.com/kb/318086