Windows XP preview program
A little late to the party but Microsoft has a page on their Windows XP preview program. Register and receive test versions (release candidates) of Microsoft's next OS over the course of the summer; the final version is due in the fall. As a bonus, the first 20,000 people will get a free copy of beta 2. Interested users should check it out here. There is also a free newsletter which will keep you up to date on all the Windows XP (formerly Whistler) happenings. The cost to register? $9.95 US.