I just noticed that the Senior Lead Program Manager for the Microsoft Store, Trevin Chow, posted the following link which allows you to pre-order Windows 7 right now. I just ordered two copies myself and got the confirmation email! So beat the rush and get it now!
UPDATE: You can also order it from Amazon.com and pay no tax.
http://store.microsoft-ppe.com/microsoft/Windows-Windows-7/category/102?WT.mc_id=trevin_blog
One thing I noticed was that it didn’t accept my Windows Live ID, however I just entered my email address in the create new account box and it went right through.

Starting tomorrow (6/26/09) you will be able to pre-order the upgrade version of Microsoft’s new operating system Windows 7. However, its only while supplies last or until July 11, so you won’t have much time to think about it. Windows 7 Home Premium Upgrade will only cost $49.99 while the Professional Upgrade version will cost $99.99 which is significant savings compared to $119 and $199 after the promo ends. It will be available from retail partners like Amazon.com, and also from the Microsoft Store. If you are interesting in upgrading, I would definitely keep an eye on Amazon.com at this page and also this one tomorrow so that you can be sure to get your hands on a copy.