First strobe what do I need to buy?

So I've been using an sb900 speed light and would like to buy a strobe for indoor shots. What do I need. I have a nikon d5000 do strobes have hot shoe triggers or is it all pc. Also do I need something to prevent the strobe from shorting out my camera. How is the strength controlled. Do I need to buy a unit to control flash strength or is it built on to the strobe unit itself like a speedlight.

Forget trying to trigger your strobe with a PC cord. That is unreliable and cumbersome, and I'm not sure if the D5000 even has a PC socket anyway. At any rate, using a physical cord to trigger studio strobes is becoming as obsolete as the 8 track tape player. All you need is a simple radio trigger. You can spend LOTS of money on these, or get one that will work fine for about $50. Here is such a unit, which I use and it works perfectly:

http://www.porters.com/porters-4-channel-flash-trigger-set-85-ft-range.html

Your strobe power is adjusted on the strobe unit itself. Your strobe power has NOTHING to do with your camera, except for the radio transmitter unit in your camera hot shoe. It sends the signal to the receiver on the strobe.

It all depends on how you like to work, I prefer manual flash, it's how I was taught many years ago, it's just easier for me, the advantage is you can use any flash with manual control (cheap). With digital it's possible to 'chimp' the shots for exposure, literally look at the screen and adjust as necessary, but a flash meter (which will cost more than a manual flash) gets around the problem with perfect exposures every time accurate to 1/10th of a stop.

The trigger voltage with some older flash units can be very high (around 300V or more) these can damage your camera beyond repair, as new manual flashes with safe trigger voltages (around the 5V mark) are cheaply available taking the risk with old flashguns just to save a few bucks isn't really an option. Flash power is adjusted on the flashgun, they all have hot shoes.

See this site which has everything you need to know about using flash off camera, the trick with flash is to get it off the camera, then you get shadows which add depth to an image.

http://strobist.blogspot.com/2006/02/welcome-to-strobist.html

Look in the 101 Archive for details.

With manual flash you can get cheap radio triggers which will sync a remote flash to your cameras Hot shoe without any wires, the RF-602 is pretty much a proven product with good build quality, 100% reliability and a range in excess of 100 Meters. They will also trigger your camera remotely with the addition of a lead from the receiver to your cameras remote input.

The much more expensive way is to use TTL flash which is automatic, these are good for 'fill in' flash and can be used creatively, but it can be a 'mind-bending' exercise when getting them to do what you want, manual flash is easier for creative work, but auto TTL flash is quicker. Add TTL radio links and you have just doubled your budget.