Data type size question, size_t, DWORD and calling assembly subroutine (Chris K)

Using PIC24, C30 what data type is "size_t", is it 16bit?It's the return value from the strlen function and also used in the MDD FSfread function. Also, how are 32bit DWORD values passed to assembly subroutines? Would W0 have the lowest 16bits, then W1..