Conditional Formatting, Create a rule?

I've built a worksheet in Excel 2007 for the purpose of tracking files that I am working on for my business. I am trying to create a rule (or something) so that whenever I type the words "YES" or "NO" a check mark or an "x" (icons) will populate instead of the text.

I've tried looking through my Dummies book and googling for "how to" but I haven't found anything that shows me how I can do this.

Is there anyone that knows what I'm talking about that can explain to me the best way to set that up?

Thank you so much!

Thank you for the quick response!

That did work. I am still wondering though, if (instead of an "X") an icon can be populated when I type "YES" and "NO". For example: 3 symbols (uncircled)