Do you just wish to score it from some other medium, such as midi, or do you wish to arrange the whole thing starting with just the basic melody?

If just score, them I suggest you use something like Finale or Sibelius. Drop a midi into you scoring program and then change it around to suit your particular band's line-up.

If you wish to completely arrange it, Band-in-a-Box is really only a good place to start the task.

Set up a March style that you like. It does not matter about the time signature at this stage, although I would be used to seeing 6/8. I find you can only score two parts at a time, so maybe trumpets with a BB harmony of choice in the Melody screen, and trombones with harmony in the Soloist screen. I would then do two copies of the tune file, each time setting up the other instruments - saxes and clarinets – with harmonies in the Soloist tracks.

Then I would drop the parts so created in Finale or Sibelius and stitch the whole thing together. Change the time signature if necessary and introduce new instruments - whatever.

It may sound like a long-winded process but it saves a huge amount of time with the harmony parts - depending on how fast you work manually of course. Anyway, it saves me heaps of time with big band arrangements.

Maybe Band-in-a-Box with be able to produce better scores one of these days, but I don't think you can use it to do the whole thing at this stage of development. And development does not seem to be heading that way.

If you are very clever using tracks you may not have to set up so many copies as I do. Stitching the whole thing together in the scoring program is a breeze.
That is my opinion. Maybe others have found a better way to work to arrive at a score with individual printed parts.

Grah Jive Talk
"Don't worry baby, they'll swing their arses off."