Maybe the comment you read referred to a difference between the 32-bit version of Windows 7 vs. the 64-bit version of Windows 7. In that case, you would need to buy the 64-bit version. Given the choice I would run 64-bit, but I still run XP 32-bit personally.
http://windows.microsoft.com/en-us/windows7/32-bit-and-64-bit-windows-frequently-asked-questions
http://windows.microsoft.com/en-us/windows7/32-bit-and-64-bit-windows-frequently-asked-questions