The ability to load a ByteArray object directly into a SWFLoader was added in Flex 3 build 187814, you may need to update your SDK build by downloading a recent nightly build from http://labs.adobe.com/technologies/flex/sdk/flex3sdk.html.

The following example shows how you can take a snapshot of an item on the display list using the static ImageSnapshot.captureBitmapData() method, which returns a BitmapData object, as seen in the following snippet:

var imageBitmapData:BitmapData = ImageSnapshot.captureBitmapData(source);
swfLoader.source = new Bitmap(imageBitmapData);

Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/11/17/taking-screenshots-in-flex-3-using-the-imagesnapshotcapturebitmapdata-method/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.graphics.ImageSnapshot;

            private function takeSnapshot(source:IBitmapDrawable):void {
                var imageBitmapData:BitmapData = ImageSnapshot.captureBitmapData(source);
                swfLoader.source = new Bitmap(imageBitmapData);
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object col1="Row 1, Col 1" col2="Row 1, Col 2" />
        <mx:Object col1="Row 2, Col 1" col2="Row 2, Col 2" />
        <mx:Object col1="Row 3, Col 1" col2="Row 3, Col 2" />
        <mx:Object col1="Row 4, Col 1" col2="Row 4, Col 2" />
        <mx:Object col1="Row 5, Col 1" col2="Row 5, Col 2" />
        <mx:Object col1="Row 6, Col 1" col2="Row 6, Col 2" />
    </mx:Array>

    <mx:ApplicationControlBar dock="true">
        <mx:Button label="Take snapshot of DataGrid"
                click="takeSnapshot(dataGrid);" />
    </mx:ApplicationControlBar>

    <mx:HBox>
        <mx:DataGrid id="dataGrid" dataProvider="{arr}" />
        <mx:SWFLoader id="swfLoader">
            <mx:filters>
                <mx:DropShadowFilter />
            </mx:filters>
        </mx:SWFLoader>
    </mx:HBox>

</mx:Application>

View source is enabled in the following example.