Paypal Express problem

I downloaded OC about a year ago. Worked with it about 1-2 months but got away.
Now I am back and need to implement my store. One big problem. I have paypal express in the payment extensions, have it enabled, and the api info in. But when you use it it will not work. The paypal express button at step 6 of checkout gives me a server not found page.

Questions:
Is this extension included in the original OC installation (1.5.6.0)?
If not, is there a way to find out (maybe some text in a file) what extension this is?
If included, does anyone know what the problem may be?

Thanks

Update:
Pay pal express seems to come with the installation. Still not working on website.
Question: Should the button work on my cart in localhost(ftp to local from web site)?

try upgrading to the latest 1.5.x version and see if it resolves the issue. The one on 1.5.6.4 should work.

no it does not work in 1.5.6.4 that is what i am using and when in sandbox mode trying to backtest all it does is take you to the normal checkout page i would like help too on this matter