I am trying to use the External URL action. Whenever I enter a url (i.e. www.google.ca) I get the following error message. Please help!

Cannotfind 'file:///G:/CSD/BUS/Common/Projects/Course Lab Test/Payments in Government/1/undefined'. Make sure the path or Internet address is correct.

How this works or not depends on the way the external site is built. Sometimes page relative referencing doesn't work so on some sites the css isn't applied.
The message you seem to have looks like the iframe object is trying to find something on your hard drive. Is this a physical drive on your PC or an external network drive, the permissions on a network drive will probably mean it won't be accessible.
I put http://www.google.ca as the external http reference and it worked OK