Read Only Fields

Can any please please please guide me as to how to set a field (or multiple fields) to be read only? I've read a couple of posts on here where you've directed people to a form post on stackoverflow.com (http://stackoverflow.com/questions/1362153/how-can-i-use-jquery-to-make-an-input-readonly), but I can't figure out how or where to put the couple of little code snippets they suggest.
It would be great long-term if GF could add a simple check-box option to each field, where you could specify a field to be read only, but short-term, is there any chance of a little bit more help here? I'm sure there would be many other (non-coding) people out there that would find this helpful as well.
Many, many thanks in advance,
Tony

David,
Thank you for the script, it works great. The only issue is if the the form isn't valid, and throws up a validation error message, the field become writable again.

Any ideas how I can stop this from happening?

Hi David

Your function works great when using in a simple form but, when included in the functions.php on a multi page form it hides the whole form (page is blank)

Hi Chris

Yes it was a javascript issue, which I sorted by only calling the script on the specific page the form shortcode was in.

Thanx for your comment.