I know somebody with a P-10 and doesn't it take full sized gum memory sticks? If so then your memory sticks wouldn't work in his equipment unless you've also got duo's in their adapter?

MemoryStick and MemoryStick PRO are both gum sized sticks
MemoryStick Duo and MemoryStick Duo PRO are around the size of a postage stamp. They're compatible with full sized memory stick equipment if you insert them into an adapter.

The difference between plain MemoryStick and PRO's is that the protocol has changed slightly to accomodate the larger flash sizes available. In theory your equipment could be firmware upgraded to support the PRO sticks but Sony is notoriously bad for upgrades.