You DEFINATELY CAN use pointers to pointers (to pointers even).
I use them with multi-dimensional arrays often.

Without seeing your RPGItem struct, I cant be sure, but try (in this order)
str_cat(_temp->name,"\ntest");
or
str_cat((_temp)->name,"\ntest");
or
str_cat((*_temp)->name,"\ntest");

The "->" is required, assuming that "name" is a string pointer.