I'd like to add an onChange event handler to the standard Contact page layout, so that when the user changes the Contact's first or last name, some JavaScript code checks to see whether there's already a Contact with that name. I'd like this code to fire when the user changes the Contact's name, and not wait until the user clicks Save.

I've read this, so I know how to create an S-control that includes HTML input tags for the Contact's first and last names, and I know how to add the onChange event handler for them. What I don't know is how to get the values of those fields saved as the Contact's first and last names when the user clicks Save.

If this can't be done in the standard page, I can write a VisualForce page. But if I go that route, can I use the <apex:detail> tag or do I have re-create the standard page layout manually, using individual inputField tags?

Thanks!