C# New Thread

Hey hello,

This is my first post so I am not sure if this is the right place for this or not but anyways...

I am trying to read a serial modem..in C#.net..and I am thinking of making a new thread for reading modem apart from the main thread which is GUI. now...I am trying to add the new thread in my form1.cs file...the code is as follows which gives me errors:

namespace WindowsApplication2
{
public partial class Form1 : Form
{

public Form1()
{
InitializeComponent();
Text = "ABC";
//Start Parrallel Thread that reads input from the Serial modem that is if
//Messages r comming in.

Thread sf= new Thread(new ThreadStart(ReadModem));
sf.Start();
.......................
.......................
......................
However I am getting an error which says type or namespace name Thread/Threadstart could not be found...are you missing a using directive or assembly reference?...

Does any body know whats goign on?
thanks.