6 Flavors of Windows 7

Windows 7 will come in 6 different versions, according to the End User blog:

Windows 7 Starter (limited to three apps concurrently)
Windows 7 Home Basic (for emerging markets)
Windows 7 Home Premium (adds Aero, Touch, Media Center)
Windows 7 Professional (Remote Desktop host, Mobility Center, Presentation mode)
Windows 7 Enterprise (available to volume license owners only, boot from virtual drive, BitLocker)
Windows 7 Ultimate (consumer customer oriented but with limited availability, includes everything)

Read more about it here on Engadget.  According to the Microsoft Blog, end users will be able to upgrade to Windows 7 directly from XP, but not with an upgrade disc.  You'll need to do a clean install.