Hoss At AOPA:
Ron is absolutely correct. You'll also want to remember, since you're using this time towards your instrument requirements, you can only use PIC XC time. You wouldn't be able to count the dual XC time from your private towards this requirement.
Just to confirm what Hoss said about the dual time during your Student Pilot days training for Private not counting towards the 50 XC PIC time, but remember that all post-Private checkride dual time does count since you're now "rated" in the aircraft. So, for example, the long IFR XC for your IR requirements counts towards that 50 as long as you make a landing somewhere more than 50nm from where you started. The only exception would be training in something in which you're not rated, say, if you were combining the IR training with ME rating training, so you were flying in something in which you were not yet rated.