I have a working demo / playable game which with a little musical work is definetly at a publishable level. I would compare it to Siberia or a similar game. What is the best step to take to get a publisher''s interest and attention?

Well you need to track down the submissions people at the various publishers and then send in a version, with all the necessary documentation (a list of documents can be found at http://www.obscure.co.uk/the_pitch.shtml)

Exactly which docs will depend on exactly how finished the game is and how much funding (if any) you are looking for. If there interested you negotiate a contract and wait for your game to appear in the shops.

Dan Marchant
Obscure Productions
Game Development & Design consultant

Submit it to garage games, or get a booth at GDC or E3.