Kevin,First off the attribute window is not customizable. But you can cycle through selected items using IEditor. The selected items that appear in the attribute window should be the same items that are selected on the map.
if (app == null)
return null;
ESRI.ArcGIS.esriSystem.UID uid = new ESRI.ArcGIS.esriSystem.UIDClass();
uid.Value = "{F8842F20-BB23-11D0-802B-0000F8037368}";
ESRI.ArcGIS.esriSystem.IExtension extension = app.FindExtensionByCLSID(uid);
IEditor3 editor3 = extension as IEditor3;
IEnumFeature enumFeat = editor3.EditSelection;
IFeature feat = null;
while ((feat = enumFeat.Next()) != null)
{
//do something
}