What was the first MacBook that people were able to install Windows on? What was the first MacBook that people were able to install Windows on? 
How about 2007, 2008 versions of Macbook?

It was when Apple started to sell MacBooks with Intel processors instead of PowerPC?
Apple introduced Bootcamp in 2006 as a beta for OSX Tiger. (source)

So it's since 2006 that the Macbooks are able to install Windows. However a support note specify that the oldest Macbooks aren't compatible with Windows 7. 

NB: Notice that laptops powered by PPC processors were called iBooks &amp; PowerBooks. Macbooks (Pro) are only powered by Intel processors.