If i aready have a sb600 .. and d3000 . ist enough to flash wireless how? i confuse

It sure will, the flash light will trigger the other flash go to bracketing and flash and set one flash as commander and the other slave
go to nikon tutorials setting up off camera flash have fun

The Vivitar 285 HV is specified to have a trigger voltage of 12V. The Nikon DSLRs are specified to be safe up to 12V. This puts the combination right at the fuzzy point. It should be safe, but if the flash goes a little high while the camera goes a little low, you might run into trouble.

The 285 (no HV) is definitely a no-go.

From the Nikon site, do you have one of these flash units.
Support for the Nikon Creative Lighting System when using SB-900, SB-600, or SB-400 Speedlights, or the SU-800 Wireless Speedlight Commander
If so You set the flash mode to "comander" the pop up flash must be UP

This Video by Nikon shows how but you will have to read the manual to get a full description go to the flash section http://www.nikondigitutor.com/eng/d300s/index.html

Then look at them all :)

As long as the camera flash is working, a slave flash will work for you. They're triggered by the light of the camera flash.

Using the auto mode on the nikon should help. It will adjust the setting automatically between night mode and day mode.

Your flash has a bad flash tube . make sure the batteries are in corectly and youhave a ready red light .

For wireless flash you need two things:

1) Something to act as the controller.

2) A remote flash.

While your SB600 will work fine as a remote flash, the D40x does not have the 'built-in' capability to act as the controller (as some of the more expensive models do). Unfortunately, you would need a SU800 or SB800 to act as controller.

Matt

Nikon hot shoe is rated up to 250V (canon's is rated up to 6V) so you can use almost any tipe of flash, except maybe for old studio flashes.
Vivitar 283 (older versions) is ~200V rated, and much lower on newer versions. It should work.

Remember that even though sb-600 is wireless, it is based on infrared. This usually means having a clear line-of-sight between flash commander and remote flash. Any object that gets in way can block signal from flash commander. Weak batteries in flash will also cause remote operation to be sporadic.

According to the manual (page 153), the DL DOES support P-TTL flash, with the built-in or external flash, but only supports high-speed flash with an external flash. What I'm wondering is, what is high-speed sync flash useful for? The only thing I can think of is fill-flash outdoors.