Is there a behavior change between SQL Server 2000 and SQL Server 2008 R2 OPTION (FAST 1)?
Yes this is just improved documentation. 

FAST n has always been the n version of FASTFIRSTROW i.e. a request to the optimiser to choose a plan that will return n rows more quickly if a plan can be identified to do so.

It is not equivalent in anyway to requesting the TOP n rows, which is in effect what you would be asking for if the expectation was for query execution to terminate after n had been delivered.