At one time FSA did make some of their cranksets compatible with Campy square taper BBs. However, AFAIK, they now only make the gossamer compact cranks for use with either mega-exo or ISIS BBs. You might be able to find the older style if you look around for old stock. It's possible, though, now that I think about it, that the *Compact* version of the Gossamers never came in a square-taper version, though.
So you have 2 Alternatives for going compact with Campy:
1. get a Campy compact crank (if you don't want to buy another BB)
Or, 2. If you get the Gossamers, you'll prob need to get the appropriate BB together with it (ISIS or Mega-Exo).