How to modify xml list item property via powershell

Hi all,

i have a sharepoint 2010 site with blog, blog contains few posts with comments. I need to modify comment property via powershel.

Have used the following code:
$spWeb = Get-SPWeb http://portal/strategy \\get the site

$dd = $spWeb.Lists["Comments"]  \\get the list of all comments
$dd.Items[1] \\ here i select required comment

Now i can see it's properties like

Xml :

<z:row xmlns:z='#RowsetSchema' ows_ID='19' ows_ContentTypeId='0x0111008F1E084351FD240821BA37C4537E336' ows_ContentType='Comment'  ows_Title='test' ows_Modified=
'2012-09-28 14:42:25' ows_Created='2012-09-28 14:29:53' ows_Author='1;#spsadmin' ... />

So the problem is so i can't modify that ows property, like ows_Created or ows_Modified via powershell.

Thanks.