Well, I dunno if you know all this so I'll give you the basics.
Over the past million years, Championship Manager was the BEST football manager game around. Nothing else came close.
However, the publisher (EIDOS) and the programmers (Sports Interactive) split up in about 2004-2005. The split saw EIDOS keep the Championship Manager name and Sports Interactive the coding.
Sports Interactive then went on to produce Football Manager 2005 and 2006. This means that Football Manager is made by the people that made the classic Championship Managers, and the current Championship Manager is only related to the classic versions by name.
So, if you want to buy a very good football manager game, make sure its Football Manager 2006.
If you want to buy a very good football manager NAME, make it Championship Manager 2006.
I wonder how many people went and bought Championship Manager instead of Football Manager, not realising the split...