ok, here is what i found about the NXT and USB with computer application, it could interest someone !
With windows 7, NXT use Winusb drivers from microsoft.
So you can use classical way to communicate with Winusb drivers : http://msdn.microsoft.com/en-us/library ... 85%29.aspx
You can also use libusb or LibusbK, I prefer libusbK because you can install a "linked driver" to existing NXT drivers on Windows 7 : http://libusbk.sourceforge.net/UsbK3/index.html
By this way standard drivers remain installed and you can use your nxt like before, and you can use the libusk library which is provided with wrapper for VB, C, Delphi.
Using libusb or libusbk permit to have an application wich will be compatible with other OS.
For my use, I remain with classical drivers and a simple Winusb wrapper I found on the web for delphi : http://winusb-delphi.sourceforge.net/
result for my usage : reading raw rgb values from color sensor stored on a mailbox by a program on the nxt with a computer application ( these values can not be obtained via direct command ).
With bluetooth : max 7 read of the value by sec with many communication errors
With USB : max 12 read of the value by sec, no errors.