A good one, there are 3 good looking tries
First try is a stalemate.
[Event "Edited game"]
[Site "RHP"]
[Date "2010.02.12"]
[Round "-"]
[White "-"]
[Black "-"]
[Result "1/2-1/2"]
[FEN "k1N4K/2R5/8/8/8/8/1p5P/8 w - - 0 1"]
[SetUp "1"]
{--------------
k . N . . . . K
. . R . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. p . . . . . P
. . . . . . . .
white to play
--------------}
1. Rc6 b1=Q 2. Ra6+ Kb7 3. Rb6+ Ka8 4. Rxb1
2nd try nearly works but Black can play 2...Kb8
[Event "Edited game"]
[Site "RHP"]
[Date "2010.02.12"]
[Round "-"]
[White "-"]
[Black "-"]
[Result "*"]
[FEN "k1N4K/2R5/8/8/8/8/1p5P/8 w - - 0 1"]
[SetUp "1"]
{--------------
k . N . . . . K
. . R . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. p . . . . . P
. . . . . . . .
white to play
--------------}
1. Rc5 b1=Q 2. Ra5+ Kb7 3. Rb5+ Qxb5 4. Nd6+
And this just fails.
[Event "Edited game"]
[Site "RHP"]
[Date "2010.02.12"]
[Round "-"]
[White "-"]
[Black "-"]
[Result "*"]
[FEN "k1N4K/2R5/8/8/8/8/1p5P/8 w - - 0 1"]
[SetUp "1"]
{--------------
k . N . . . . K
. . R . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. p . . . . . P
. . . . . . . .
white to play
--------------}
1. Ra7+ Kb8 2. Nd6 Kxa7 3. Nb5+ Kb6 4. Nc3 Ka5 5. h4 Kb4 6. Nb1 Kb3 7. h5
Kc2 8. Na3+ Kb3
So solution is as posted by meadows
[Event "Edited game"]
[Site "RHP"]
[Date "2010.02.12"]
[Round "-"]
[White "-"]
[Black "-"]
[Result "*"]
[FEN "k1N4K/2R5/8/8/8/8/1p5P/8 w - - 0 1"]
[SetUp "1"]
{--------------
k . N . . . . K
. . R . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. p . . . . . P
. . . . . . . .
white to play
--------------}
1. Nb6+ Kb8 2. Rc3 b1=Q 3. Nd7+ Ka7 4. Ra3+ Kb7 5. Rb3+ Qxb3 6. Nc5+