IMHO, a 30mm shorter axle-to-crown dimension will make a huge difference in handling, especially on a bike with small wheels. You will also lower your bottom bracket significantly.
I fitted a suspension corrected fork (extra 30mm a-to-c, 559 wheels) to a frame not designed for suspension in a deliberate attempt to kick out the geometry on my Xtracycle. It worked, but I noticed the elevated bottom bracket height immediately too. Not what I wanted, but is only a minor nit. Lowering it would have been bad though.
It you still decide to use that fork with a threadless headset, you can use the seat post clamp trick a-la Sheldon Brown's IRO (Google it). Use a seat post clamp. If you can't find one without the lip that prevents the clamp from sliding down the seat tube, you need to take a Dremel tool to it. You'll still need some way to pre-load the headset before tightening the seat post clamp. You LBS should be able to use normal spacers in conjunction with their headset press to do this with the fork in place.
Good luck.
Last edited by sqynt; 04-22-09 at 01:47 PM.