Installing multiple conversion tracking codes on same page

We’re advertising on Google, Yahoo and MSN. I have an order confirmation page that I want to install conversion tracking code on for all 3 of them.
Do I need to code something that will only run the Google conversion tracking script if the person came from Adwords? Or is it okay to run all 3 scripts at once regardless of where the conversion came from?
I just don’t want Yahoo claiming a conversion if the buyer actually came from Google.
Anyone with experience on this one?

See original post by aqgiles