Hi James,
No, problem, I'll try to help you where I can, so is it that you just need a basic guide on how to test (in particular assert content/status codes) for RESTful webservices with SoapUI?
If so, there are plenty of other options in addition to that video in the SoapUI doumentation?
I found these (haven't whatched the videos, but the blog looked like it might help):
http://www.joecolantonio.com/2012/09/05/soapui-how-to-test-a-rest-service/
https://www.youtube.com/watch?v=XV7WW0bDy9c
https://www.youtube.com/watch?v=uvrpjqPJDUU
https://www.youtube.com/watch?v=7YpJS--BqiI
Of course there are books too and other great blogs!
I haven't looked at the official SoapUI documentation for a little while, did have a quick look at http://www.soapui.org/getting-started/rest-testing.html (was that the one you mean't?). Without commenting too much, I did notice a fair few references to the pro / NG version, which is understandable given Smartbear look after the open source versions... but, fear not, there is no obstacle to do what you need with the open source version, millions do!
In your case, can't give you much more detail unless you provide a sample response, but to check for error messages for Rest Request TestSteps I would suggest:
Valid / Invalid Status Code Assertions (under Compliance, Status & Standards assertions)
XPath Match (under Property Content assertions)
Also, if you're confortable with Groovy script:
Script Assertions - you can do pretty much most things with these!
See also http://www.soapui.org/functional-testing/validating-messages/getting-started-with-assertions.html
Cheers,
Rupert