Just do a Web search on "threadless headset spacers"; they go from cheap to expensive. You don't have to cut your steerer, you will just need to stack spacers above and/or below the stem so that they are 3mm to 5mm above the steerer. The top cap MUST bear on the spacers or stem NOT the steerer if you are to correctly adjust the headset. You can then shuffle spacers and the stem around until you find a height that you like; you can then cut it (or not) at the height you wish.

Here is an alternative method which does not use spacers to set the adjustment: http://sheldonbrown.com/handsup.html#threadless

You can even mount two stems with this method: http://sheldonbrown.com/org/thorn/index.html