сделай датасет паблик и будет тебе счастье

namespace
{
public class cfmMain : System.Windows.Forms.Form
{
public DataSet ds;
FrmB29 B29;
private cfmMain()
{
B29 = new FrmB29(this);
}

/////////////////////////////////////////////////////////////////
//// остальные переменные свойства и методы /////////
////////////////////////////////////////////////////////////////
}

public class FrmB29 : System.Windows.Forms.Form
{
private cfmMain Owner;

public FrmB29(cfmMain owner)
{
Owner = owner;
}
public WorkWithDataSet()
{
Owner.ds.ReadXml(@"c:\data.xml");
}
/////////////////////////////////////////////////////////////////
//// остальные переменные свойства и методы /////////
/////////////////////////////////////////////////////////////////
}
}

formOwner.da_dUser.Fill(cDataSet1,"user");
cDataSet1=formOwner.ds_dUser;
foreach(DataRow dr in cDataSet1.Tables["user"].Rows)
{
Name.Add(dr["Name"]);
}

2>M234

ну можно и так, хотя компакт фреймворк этого не поддерживает :))

Supported by the .NET Compact Framework.

[Visual Basic] Overloads Public Function ShowDialog() As DialogResult
[C#] public DialogResult ShowDialog();
[C++] public: DialogResult ShowDialog();
[JScript] public function ShowDialog() : DialogResult;

Shows the form as a modal dialog with the specified owner.

[Visual Basic] Overloads Public Function ShowDialog(IWin32Window) As DialogResult
[C#] public DialogResult ShowDialog(IWin32Window);
[C++] public: DialogResult ShowDialog(IWin32Window*);
[JScript] public function ShowDialog(IWin32Window) : DialogResult;