When first trying to run your own scripts, you may get:

File C:\SomeFolder\SomeScript.ps1 cannot be loaded because the execution of scripts is disabled on this system. Please see "get-help about_signing" for more details.

To allow unsigned scripts to run, you need to run (from Start > Run > "Powershell"):

ps> executionpolicy

(you should see you are currently set to restricted), so can change using:

ps> executionpolicy remotesigned

or

ps> set-executionpolicy unrestricted

You should then see:

Execution Policy Change
The execution policy helps protect you from scripts that you do not trust.
Changing the execution policy might expose you to the security risks described
in the about_Execution_Policies help topic. Do you want to change the execution
 policy?
[Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"):

To which you say yes. Once this has been done, you should be able to run your own scripts.

NB To see more detail on the various execution policies, and the security associated with changing it, please see:

http://www.windowsecurity.com/articles/PowerShell-Security.html