Pafl: I used 2 engines for helping in my short analysis, for checking my ideas and to find some new ones too......: Ikarus V0.18 and my favourite CM9000-JudgeII.
The JudgeII found a way for winning but Ikarus also had some good ideas..........

So the "party" for black begins with 19...Nxh2! instead of 19...e4?
After it white has to play 20.Ke1 and then 20...Nf3+ 21.Kd1 which is forced.
Then there are 2 moves:

21...Nh4+ 22.Kd2 Qf2+ 23.Kc3 Qxg3 and black has 2 Pawns more and a win is reachable........(The continuation 24.Rg1 Qf3 25.Bxf7?! Qxf7 26.Rxg4 Qf6!? winning a Pawn back is not good, as white has huge problems in the Kingside due to possible advance of black Pawns with h5, but the most important is that black can play Nf3 and then e4 is killing....)

21...0-0-0 and now there are 3 choices for white:

** 22.Nc3 and then 22...Qc6! and white has many problems to solve so he can't survive........

** 22.Na3 and then 22...h5! and black has a very dangerous attack and a very cramped position [edit]for white[/edit].........There are too many threats!
After 23.c3 (for letting the King escape via c2) there is 23...Ng5+ 24.Kc2 Qf2+ 25.Qd2 Qxg3 26.Rg1 Qf3 -+

** 22.Ne2 and then 22...Qc6! -+ Black is winning clearly!