7/2008 is a number, 7 divided by 2008 = 0.0001429 I doubt that's what you wanted.
Just for clarification, a date is the number of days since 1/1/0001.
It actually is 7 dividied by 2 divided by 2008 because 7/2/2008 is seen as text. But I meant that TRUE FileMaker dates are the number of days since 1/1/0001. If you want to address a date field in a calculation, FM must see it as a date so you need a date function such as Date().
If ( CDATUM = Date ( 7 ; 2 ; 2008 ) ; 200801 ; 0 )
However, I am unsure why you care hard-coding a date into a calculation field,