Hi Ravi..
No issue in it.. It is very Simple..
Just give this code in your text box control..
style="resize:none"
as shown below...
<asp:TextBox ID="txtProperShippingName" TabIndex="35"
runat="server" MaxLength="120" Width="96%" TextMode="MultiLine" style="resize:none" Rows="3">
</asp:TextBox>