Output the nth digits of an integer
GolfScript (10 bytes)

~(\10base=


This assumes input is as a string (e.g. via stdin). If it's as two integers on the stack, the initial ~ should be removed, saving 1 char.

If the base conversion is considered to fall foul of the built-in functions rule, I have a 16-char alternative:

~~)\{}{10/}/=10%