Microsoft has released Windows XP RTM (Build 2600) to the beta testers. Thanks NaTaN.

The follow version are available:
Windows XP Home Edition (180 day beta version)
Windows XP Professional (120 Day Evaluation version)
Windows XP Professional Checked Version (For Developers)
Windows XP Professional 64 Bit (180 day beta version)
Windows XP Professional 64 Bit Checked Version (For Developers)

Visit Windows Beta Website