how to put Prompt Text into a textfield

Hi -

anyone able to give a brief "howto" for putting Prompt Text into a textfield? (you know, the text in a textfield that says 'search' for a searchbox and then goes away on focus? makes for a nice, compact form)

Outside a cms I'd put the attribute value="search" in the input tag. I'm still not so skilled that I can figure out how to do it with overrides (I'm using that word without having more than a superficial understanding of it, btw, and have not yet been able to climb the learning curve enough to accomplish my little task... other curves to climb keep jumping in front of it!).

Searched thoroughly and checked on irc before posting here (and you're right: everyone should be thorough - if nothing else the forums/issues would be easier to search if there were fewer repeated topics); happy to search again if anyone has better keywords to use....

Thanks in advance!