I am animating a camera inside a quite tight boundary of objects. Navigating though the IPO and continuously checking if the interpolation is correct and I don't go inside an object is tedious.
is there a way to show the interpolated spline in the 3D window? so it would be easier to check the camera position between keys. Showing the keys dotted on the spline would be useful too.
Or maybe this option exists and I don't know how to activate it?

not really

the closest thing is to turn on dupliframes in the animation buttons
(object buttons in 2.30 or later)

you have to turn them off to edit the keyframes/curve though

also, this would have been better posted on www.elysiun.com than here because this forum is intended for developers, the one on elysiun for users