populate datagridvie from xml

Hello All
Need help with LINQ
I have this sticky issue with using select statements from within my code . I dont know how to use one.
The code for the method and the xml structure are as attached.
This is part of the code

public void PopulateGrid(DataSet dataSets, String tableName,String testStepId)
{
this.dataSet = dataSets;
//'this' here is a usercontrol - an Editable Data Grid View to be precise.
IEnumerable<Int32> dfp2 = from paramss in dataSet.Tables["Parameters"].AsEnumerable()
where (paramss.Field<Int32>("TestStep_Id") == Int32.Parse(testStepId))
select paramss.Field<Int32?>("Parameters_Id");

var p2 = from parameter in dataSet.Tables["Parameter"].AsEnumerable()
where parameter.Field<Int32>("Parameters_Id") == (Int32)dfp2.First()
select parameter;

// bindingSource.DataSource = parameter.AsDataView();
bindingSource.DataSource = p2.AsDataView();
.
.
.
.
}

And this is my xml file

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if setCTRatio == getCTRatio testResult.valid = true else testResult.valid = false end

As you can see there are two teststep commands {SetCT and ReadCT } and each has a parameter to it .
My app has two data grid views - one for test steps and the other for parameters pertaining to those test steps. So whenever i click on one of the test steps , i populate the second data grid view with paramters pertaining to the clicked test step.{The above code populates the data grid view for paramters NOT test steps}
How do i frame my select statement so as to be able to get the parameter pertaining to the test step that i have clicked? Is there a better way to do it than what is mentioned above?
Thanks
Avink