Java, 76 or 31
Counting only the insertions made to the code, ignoring new lines. 76 if you count everything I've added, 31 if you exclude the first line and the last line, i.e. only counting int a=1/0;try{}catch(Error e){}. (Which is what the other answer does.)
class P{public static void main(String[]A){ try { while(true) try { int a=1/0;try{ } catch(Exception ex2) { } } catch(Exception ex1) { // your goal is to reach this catch block by modifying the code ... // in the inner try block above // You win if you reach this part and execute on of the following code lines //Console.WriteLine("You won!"); // for C# // Or System.out.println("You won!"); // for Java } }catch(Error e){} }}