Pentax, I am bit surprised that you said there was no perspective tool. But I think I know why you couldn't find it so do read on ...
When you select the crop tool you will NOT see the perspective check box. However, first make your crop selection and THEN you will see the check box as shown below. Check this, now adjust the sides as per the tutorial and it will all work for you
Apologies for not mentioning that in my original tutorial.
Cheers,
Rob