Er, as far as I know, the three CSIs have never all been in the same episode.
CSI had a crossover with CSI:Miami entitled 'Cross-Jurisdictions'. It was CSI's season two (ep 22) and CSI:Miami's season one. This was the beginning of CSI:Miami.
CSI:Miami had a crossover in season two with CSI:NY entitled 'MIA/NYC-Nonstop'. This was the beginning of CSI:NY.
CSI:Miami then had another crossover in season four entitled 'Felony Flight', which was part one of the crossover. It continued the next night on CSI:NY, entitled 'Manhattan Manhunt.'
So far, the original CSI has never had another crossover except with 'Without a Trace'.
For future questions about all three shows, please visit the
I Still Have A Question thread in the
General CSI forum.
^ Oop, I was posting the same time you were, heh.
And
CSI2008, please don't spam up the boards with the same question.
*locked*