C: 120
=

    o,c,l;main(n,i){for(scanf("%d",&n),i=3,l=2;o<n;for(c=2;c<i&&i%c++;),l=c==i?o+=i==l+2,i:l,i++);printf("%d, %d\n",l-2,l);}

Sample run:

    $ for i in $(seq 1 10); do echo $i | ./twinprimes; done
    3, 5
    5, 7
    11, 13
    17, 19
    29, 31
    41, 43
    59, 61
    71, 73
    101, 103
    107, 109