There are two differences between define and typedef.

Firstly, typedef obeys scoping rules just like variables, whereas define
stays valid until the end of the file (or until a matching undef).

Secondly, some things can be done with typedef that cannot be done with define.
Examples:
Code:
typedef int* int_p1;
int_p1 a, b, c;  // a, b, and c are all int pointers.

#define int_p2 int*
int_p2 a, b, c;  // only the first is a pointer!
Code:
typedef int a10[10];
a10 a, b, c; // create three 10-int arrays
Code:
typedef int (*func_p) (int);
func_p fp // func_p is a pointer to a function that
          // takes an int and returns an int