Need help to Automate RESTServices with JSON input .

Hi all,
I am new to SoapUI. I have downloaded the new version 4.6.2.
Here I have to test a RESTFull webservice with JSON input.
MY JSON input is
{
"OSversion":"XP";
"userid":"siva";
"appversion":"1.0";
}

Here I that output of REST webservice is JSON content.
Here I have to give different inputs by changing OSversion and appversion.
So how Can I automate these things using SoapUI.
Can I write any java code or Groovy script to automate the above functionality?
Please provide the guidelines.

Thanks in Advance
Siva Ganesh