TechSoup has a good little article discussing the pros and cons of upgrading visit http://www.techsoup.org/learningcenter/software/page12222.cfm

Briefly they say:

• Make sure your hardware will support Windows 7;
•  Make sure your programs will run on Windows 7

 If you are upgrading from Windows XP -  You can’t upgrade directly. Unfortunately, Microsoft has not provided Windows 7 with the capability to upgrade directly from Windows XP. The explanation is that so much has changed between Windows XP and Windows 7 within the operating system kernel itself, the Registry, the drivers, etc. that trying to get from Point A to Point B just won’t work. That isn’t as horrible as it sounds. Frankly, although in-place upgrades are convenient, experts always recommend doing a fresh install when moving to a new operating system in order to ensure the best performance and overall experience.  Visit here http://www.cnet.com.au/upgrade-windows-xp-to-windows-7-339299114.htm  for more information.

 If you are upgrading from Windows Vista – If you’re upgrading from Windows Vista to Windows 7 it should be a fairly easy install. You can do what’s called an in-place upgrade as long you install the same version of Windows 7 as you have of Vista. For instance, if you have Windows Vista Home premium you can upgrade to Windows 7 Home Premium. 
Visit here for more information http://www.cnet.com.au/upgrade-windows-vista-to-windows-7-339299167.htm

 TechRepublic has a also has a good article on planning and preparing for the migration. http://blogs.techrepublic.com.com/10things/?p=1000&tag=nl.e101 .

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