If you want maximum contrast then a single light with no modifier is the way to go.

However the shots you posted don't show that sort of contrast and have a lower contrast smooth transition from highlight to shadow, which is the hallmark of a large diffused lightsource, such as a softbox or shoot through umbrella.

Definitely go with a strobe over a continuous lightsource as it means you can overpower the ambient light so it doesn't show up in your shots.

You have two main options: a studio (mains powered) strobe kit or a battery powered hotshoe flash based setup (usually the parts are sold separately but can be available in kit form).

A studio kit will usually comprise two heads, two stgands, two softboxes/umbrellas and sync cables. That's all you need to get shots like the ones posted (except for the smoke, unless you go for a really cheap kit and one of the heads explodes).

For the hotshoe approach you need at least one flashgun, one stand (a tripod will do) and some method of triggering the flash (cheap radio triggers are available from ebay and work ok most of the time :)

The advantages of this approach are: price (the hotshoe setup is more modular, and you can build it up over time for a lower initial investment), portability/flexibility, the gear is lighter and doesn't need to be plugged into the mains.

The advantages of the studio approach are power, better light from softboxes rather than umbrellas (more control, less spill, can get closer), syncing with cables more reliable than wireless.

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Given that you already have an SB800 I would go with that and buy a lightstand, umbrella holder and white shoot through umbrella. You can get great results with one light if you know what you're doing, so the next most important thing is to practice on a willing volunteer first.