Ahhh what's going on here?!?!? Ok ok ok..the sync speed refers to the on camera flash only. With a flash like the sb-600 on the D90, you can shoot at any shutter speed, and this is the same with the strobe off camera. There is a setting, and it's in your manual. That's how I found mine.
I just love it when people post things and don't explain what they are talking about.
If your camera is connected to your flash be it a sync cord or the hotshoe you have a certain shutter speed that your camera will sync at. For the D90 it is 1/200.
Except that the Nikon D90
can sync with a Nikon speedlight at
any shutter speed using
Auto FP High-Speed Sync, even at incredibly fast shutter speeds like 1/8000th, and it
can be done through a sync cord if that sync cord supports iTTL, or a hotshoe, or using iTTL Commander type arrangements for wireless off-camera flash, as long as both the camera and speedlight gear support Nikon's "Auto FP High-Speed Sync", which it is my understanding that all their modern DSLR and speedlight products do.
Supported Nikon cameras and speedlights as of a year ago, October 2008:
NIkon SB-900
Nikon SB-800
Nikon SB-600
Nikon SB-R200
Nikon SB-28DX
Nikon SB-80DX
Nikon D80 (#25: Auto-FP: On / Off)
Nikon D90 (e1 in CSM)
Nikon D200 (e1 in CSM)
Nikon D300 (e1 in CSM)
Nikon D700 (e1 in CSM)
Nikon D2H / D2Hs (e1 in CSM)
Nikon D2X / D2Xs (e1 in CSM)
Nikon D3 (e1 in CSM)
Nikon D3H (e1 in CSM)
Nikon D3X (e1 in CSM)
Canon has the same capability, and I've sync'd my 40D and 580EX-IIs at all kinds of speeds, into the thousandths of a second, other than the normal sync speed of 1/250th, including the use of ETTL sync cords to get the light off-camera while doing it.
Again,
IF IT'S IMPORTANT for this Nikon D90 photographer to get high-speed flash syncs for
their photography needs, that capability
does exist - there is no ball and chain locking them down to 1/200th and nothing else.