Can't say for sure as I've not found any cases, skins or covers specifically for the N900 yet, but the rubberized hard cases I saw for the N97 come in two pieces. I know the N900 is slide vs tilt and slide however, I'd imagine the same sort of thing will become available for the N900.

One piece goes around the edge of the screen with holes for buttons, ports, etc. The other covers the back and sides of the keyboard with holes for camera, ports, etc.

Google or ebay for "n97 rubberized hard case" for pictures.

I hope there's a case and screen protectors for the N900 soon. I'd like to pre-order them to arrive with the phone as I'm guaranteed to drop or scratch it if I don't have them!