I am not sure what code to post - here is a start:

From the intialize section of the main form
//
// pnlControls
//
this.pnlControls.Anchor =
((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top

           | System.Windows.Forms.AnchorStyles.Left)
           | System.Windows.Forms.AnchorStyles.Right)));
this.pnlControls.Location = new System.Drawing.Point(0, 0);
this.pnlControls.Name = "pnlControls";
this.pnlControls.Size = new System.Drawing.Size(w, h);
this.pnlControls.TabIndex = 0;
this.pnlControls.Paint += new
System.Windows.Forms.PaintEventHandler(this.pnlControls_Paint);

menu item that loads the panel with the user control "ucTaxAdjustment"
private void menuItemTaxAdjustment_Click(object sender, System.EventArgs e)
{
    if (!pnlControls.ControlExists(controlName_TaxAdjustment))
    {
        this.pnlControls.AddControl(new
ucTaxAdjustment(),controlName_TaxAdjustment);
    }
    this.pnlControls.ActiveControl = controlName_TaxAdjustment;
}

Load event of the user control
private void ucTaxAdjustment_Load(object sender, System.EventArgs e)
{
    Dock = DockStyle.Fill;
    if (this.pnlCompany.Controls.Count == 0)
this.pnlCompany.Controls.Add(ucCS); //loads another user control on a panel
on this user control
}

thanks