Windows 7 Home Premium 64 does not support some older software such as QuickBook 2006 and Adobe Professional 7. To install them, I need Windows XP mode, which only comes with Windows 7 Professional, Ultimate or Enterprise.
I tried to upgrade Windows with Windows 7 Ultimate CD. However, that required a fresh installation, which would wipe out my existing programs. Lucky, Windows 7 provides and Upgrade Any Time feature. You can click on it and purchase the upgrade online. With this upgrade, you keep your exiting programs. I upgraded my Windows 7 Home Premium to Windows 7 Professional, which offers Windows XP mode.