J, 12 characters

":@(!{:)\@i.

J, 12 characters

":@(!{:)\@i.

   i.5
0 1 2 3 4
   {:i.5
4
   (i.5)!{:i.5
1 4 6 4 1
   (!{:)i.5
1 4 6 4 1
   (!{:)\i.5
1 0 0 0 0
1 1 0 0 0
1 2 1 0 0
1 3 3 1 0
1 4 6 4 1
   ":@(!{:)\i.5
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
   (":@(!{:)\@i.)`''
+----------------------------------+
|+-+------------------------------+|
||@|+-------------------------+--+||
|| ||+-+---------------------+|i.|||
|| |||\|+-------------------+||  |||
|| ||| ||+-+---------------+|||  |||
|| ||| |||@|+--+----------+||||  |||
|| ||| ||| ||":|+-+------+|||||  |||
|| ||| ||| ||  ||2|+-+--+||||||  |||
|| ||| ||| ||  || ||!|{:|||||||  |||
|| ||| ||| ||  || |+-+--+||||||  |||
|| ||| ||| ||  |+-+------+|||||  |||
|| ||| ||| |+--+----------+||||  |||
|| ||| ||+-+---------------+|||  |||
|| ||| |+-------------------+||  |||
|| ||+-+---------------------+|  |||
|| |+-------------------------+--+||
|+-+------------------------------+|
+----------------------------------+

J, 17 characters

Assuming n is already defined,

":@(i.!#~)"0>:i.n

If not, replace n by ".1!:1]3 to read from stdin (24 chars).

J, 12 characters

":@(!{:)\@i.