Chairman Meow
Class IV
Windows ME is effectively Windows 2000 Home.
Not really... Windows ME is Win9X/DOS-based, but Windows 2000 (in addition to all later versions of Windows*) is NT-based.
*Except Windows CE, which doesn't count.

As for the original topic of the thread, considering that buying a copy of Vista would cost a couple hundred dollars (unless you get it with a new computer, but a new computer will cost several hundred dollars), perhaps the question should be "Could someone explain why I should get Vista?"