Int(6 * Rnd) + 1 is correct. (There is no need to specify an argument to Rnd.)
Rnd is evenly distributed in the range 0 <= Rnd < 1.
Rnd * 6 is evenly ditributed in 0 <= (Rnd * 6) < 6.
Int rounds down, so Int(Rnd * 6) is evenly distribted in [0, 1, 2, 3, 4, 5].
Adding 1 gives you a result evenly distributed in [1, 2, 3, 4, 5, 6].