There are three ways to get a still into a project:
1) The motional control camera. The most expensive method, there are houses which specialize in this. You can zoom, pan, etc.
2) Shoot the stills with a motion picture camera. This is great when you can't take possession of the original. The downsides are the difficulty lining the camera up so the image doesn't 'keystone', lighing the image so there aren't reflections or glares, and the quality of the camera moves. You're typically working a long lens, so any movement in the camera is exaggerated, zooms are difficult, and if the image is really small and you're using a macro lens, you can't zoom anyway.
3) Scan and manipulate in post. I like this method the best, especially since I hate shooting stills. If you scan at a high enough resolution, you can zoom in quite a bit without exceeding the resolution of video. I'm working on a HD documentary where the director is scanning every still he's planning on using. So far, on NTSC versions of the project, everything looks great. He scanned the images at a very high resolution, so he can push in two or three times the actual size and theoretically still exceed HD resolution. We'll see.
I think that scanning is a good option, just make sure you create files at a high enough resolution.