`Now think about it: a piano. The keys start. The keys finish. You know there are 88. On this no one can fool you. They are not infinite. They are not. You are infinite. And, inside those keys, the music you can play is infinite. They are 88. You are infinite. I like this. I can live this."

So says Danny Boodman T.D. Lemon 1900, the eponymous star of Italian writer Alessandro Baricco's play 1900 - The Pianist on the Ocean, translated by Marella Boschi. The English-language world premiere opens tomorrow in the Civic Theatre, Tallaght, in a co-production with Common Currency Theatre Company.

I play 1900's trumpet-playing friend, Tim Tooney, who tells the bizarre and gripping story of the pianist born on the Ocean. It's directed by Leticia Agudo, from Seville, with a five-piece jazz band playing music composed by prodigious keyboards wizard Justin Carroll.

I've been lucky to be involved in productions with some of the best piano-playing composers around. Trevor Knight composed the music for my one-man play Catalpa, and he always performs with me. (In fact, on Saturday we did a recital version in Copenhagen). And this time last year, I worked with Conor Lenihan in The Tempest in the Abbey.

I love watching the magic of music composition while it's happening. It always involves a hell of a lot of "I don't know". I love it when people say: "I don't know". That means the process is a journey, not a made-up destination. It's evolving organically, not being manufactured artificially.

Of course, the silent qualification is "yet". The time of knowing, and knowing full well, will come, you can bet on it.

Another thing I've noticed is the random way in which ideas spring up, very often outside "real" rehearsal time. And I don't just mean in the pub afterwards.

Of course, it's because our heads are full of the stuff morning, noon and night. We're sad obsessives.

At time of writing, we're just reaching the end of the last week of rehearsals. Rehearsal time is a bit like 1900's description of a piano. It starts; it finishes; it is most definitely not infinite; but the hope is that the imaginary world you generate within that time is infinite.

Really, it's down to the eternal struggle, in life as much as in art, between limits and freedom. You can't achieve real freedom of artistic expression without the limits of discipline; the limits of discipline are a waste of time unless they facilitate your freedom to express.

Rehearsals usually involve a messy mixture of rigorous discipline and fairly free-wheeling experiment. The first session with Leticia, Justin and myself was what feels like years ago - sometime in August in Justin's parents' house.

The Carrolls are the epitome of the musical family. When the front door opens you expect a cymbal to roll down the garden path. The back room has a grand piano in the corner, at least two computers, what seems like several drumkits, the furriest cat I've ever seen and an overwhelming array of amps and speakers for you to sit on.

Justin's brother, Ray, was just finishing a rehearsal. I got the definite feeling we were about the fifth group to use the Carrolls' backroom that day. Thanks for the tea, Mrs Carroll.

It was one of those essential rehearsal times where we spent a lot of time asking questions, saying "I don't know" and then trying stuff out anyway. Gradual progress towards an unknown destination. I love those kind of sessions. What you gain is intangible but you leave with far deeper knowledge of the journey you are on than you had when you arrived.

WE met for the second time in a room in Belvedere College a few weeks later, along with the other musicians: Brendan Doyle on clarinet, Ray Martin on trumpet, John Moriarty on guitar and Dan Bodwell on double bass.

We ran through some of the more obvious set-pieces in the script, which were begging for musical accompaniment. It was good fun. Bringing the two together: the text and the music; sliding them up against each other; speeding the text up; slowing the music down; starting here; fading there. It's great fun. Everybody is buzzing a little bit after it. Well, I am anyway.

Then came the first session in the rehearsal room with Justin on the keyboard and me (supposedly) off script. It's hell. For the first hour, I can't even hear the music - just some grinding, faraway noise trying to stop me remembering the lines. Then, gradually, I'm able to let it in. I can hear it and it infuses what I'm saying. The whole thing starts to feel like maybe it has wings if I can find out how to spread them.

The first rehearsal-room session with the full band. It's a shock to hear such a Big Sound, having got used to just Justin's keyboard in the corner of the room. As usual, the lines fly away into the blue yonder for half-an-hour but after a couple of try-outs they come back and start to swirl around the music. There's a sense of pressure with so many people in the room but it's welcome pressure.

And then the magic moment happens when the band coming in isn't an ordeal to be overcome anymore but an opportunity to have fun. It's like having a warm wind in your sails. It's like surfing on a strong wave. It's exhilarating and makes you remember why you like doing this stuff in the first place.

The lines stop autocueing in front of your eyes and become live, infused with new, unexpected meaning. You can start playing - going with the music; going against it. It all starts to happen in a non-logical way; your body does things your mind doesn't tell it to.

Your voice flies off in unexpected directions. I still fall flat on my face every now and then but it's easy to get up and continue. It doesn't feel like work. It feels like play. Play with music.

1900 - The Pianist on the Ocean opens tomorrow night at the Civic Theatre, Tallaght, and runs until Saturday. Also from November 27th to December 2nd