Parallel execution is an attribute of the test runner and has got nothing to do with selenium.
If you are able to run a regular xUnit test in parallel then you should also be able to do it for selenium tests.
Sometime back I wrote up a blog post which shows you how to do this in Java.
https://rationaleemotions.wordpress.com/2013/07/31/parallel-webdriver-executions-using-testng/
Hope that can help you get started.
-Krishnan Mahadevan
"All the desirable things in life are either illegal, expensive, fattening or in love with someone else"