Hi Roc,
You can either freeze the motion using the shutter in continuous or "ambient" light, or x out the ambient and freeze the motion with flash. A typical studio setting on your camera in manual mode of say 1/160 at f/8 and ISO 100 will get rid of most ambient lighting (ie if you take a shot without the flash at these settings, you'll get a black frame). You need to keep the shutter speed below about 1/200th as above that, you get a moving slit and normal flash operation is not possible. High speed sync just turns your speedlight into a big torch and wastes most of the light, and I'm not going to go into details of that here as it's not the way we freeze motion in the studio.
Speedlights control their light output by varying the duration of the light, using an "Insulated Gate, Bi-Polar Transistor" - or "switch" :/. This is good and bad for freezing dancers.You can get fast flash durations but at lower light outputs. My Nikon SB900 speedlights for example put out about 70 Joules (or "watt-secnds") at full power. At full power, the duration is about 1/900th of a second. Not really enough to completely freeze flour. At half power, it will be about 1/1500th and at one quarter power (2 stops below full power) it will be about 1/3000th of a second. This is short enough to freeze most flour and dance and is a good target to aim for.
However, now I only have 15 Joules of light coming out of my speedlights. I could increase the ISO and/or open the aperture but that lets in more ambient light. If you shoot in a dark room, this will work just fine - raise up the ISO, open up the aperture and dial the flashes down to 1/4 power. I used to use 4 SB900's shot into one 5ft brolly to get 70 watt-seconds of light at 1/4 power. It's enough, but limits your lighting arrangements.
Lencarta Superfast studio flashes work in the same way as speedlights, but you start with a much bigger number for light output (about 600 Joules) and here's a series of 3 posts and video on using those:-
http://owenlloydphotography.com/?p=1685
http://owenlloydphotography.com/?p=1699
http://owenlloydphotography.com/?p=1732
