This question has been asked before here. If you are using Firefox all you have to do is make the textbox "readonly", however IE doesn't gray as good as firefox. You have to use CSS to get the desired color. Below is style I applied. Couldn't spend more time to get the border color right.
To change the color on the fly you can create a named style and assign the class attribute of the textbox.
You have more than one way to create gray text box, but you need CSS. [ March 01, 2007: Message edited by: Purushothaman Thambu ]