Assign SiteGroup to SiteUsers Webpart via PowerShell

Hi,

our subsites will be created via PowerShell. It will be used a Template,  with a SiteUser Webpart on the home page. In that Webpart should be displayed a site-specific Group, created in PowerShell too.

How to put the Group into the Webpart :  how to get the Webpart and how to set the appropriate Attribute ?

Thanks,

Michel