Good timing on the WP forum!
I've been googling ways to add Adwords Conversion tracking code to WP and the best method so far seems to be to create a custom 'thankyou' page with the conversion tracking code on it and redirect the contact form to it. I'd prefer the code to be on the actual contact page though, you get a few more false positives that way but you'll also pick up people who only wanted the phone number instead of just the poeple who email.
Seems a bit bodgy though, just wondering if any WP experts on here know a better way? In Joomla it would be as simple as creating a module and only allowing it to be active on the contact page, dead simple, can't believe it's not that easy with WP?