That sounds like a lot but most consumers will only be confronted by the Home Premium and Professional SKUs. The Starter edition is only for OEMs, Home Basic is only available in emerging markets, Enterprise is for enterprises only and the Ultimate edition will have limited availability.
Engadget published a list with the differences of the six Windows 7 SKUs:
Windows 7 Starter
Windows 7 Home Basic (Vista equivalent: $200)Available worldwide to OEMs on new PCs Missing Aero UI tweaks Limited to 3 simultaneous applications
Windows 7 Home Premium (Vista equivalent: $260)Only available in emerging markets Missing Aero UI tweaks
- Available worldwide, to OEMs and in retail
- Includes Aero UI tweaks
- Features multi-touch capabilities
- Adds "premium" games
- Adds media capabilities (Media Center, DVD playback, DVD creation, etc.)
- Can create home network groups
- Available worldwide, to OEMs and in retail
- Includes all features of Premium
- Adds enhanced networking capabilities (Remote Desktop host, domain support, offline folders, etc.)
- Adds Mobility Center
- Adds Presentation Mode
- Available only in volume licenses
- Includes all features of Professional
- Adds Branch Cache
- Adds Direct Access
- Adds BitLocker
- Limited OEM and retail availability
- Includes all features of Enterprise