Formula result dependant on date?

[ddub25]

=IF(B958="","",IF(E958="post",0,IF(E958="pre","?",IF(E958="n/a","n/a",IF(E958="","?")))))

Is it possible to incorporate into this formula that,

IF X958 contains a date before 13/08/2011 (13th Aug 20011), return "n/a"

Thanks in advance.

Dan

 

[VoG]

Possibly

=IF(X958<"13/08/2011"+0,NA(),IF(B958="","",IF(E958="post",0,IF(E958="pre","?",IF(E958="n/a","n/a",IF(E958="","?"))))))