how do you mean by "cannot support certain format"? DX is the "cropped frame" format while FX is the "full-frame" format. nikon has support for both.
if your talking about compatibility of camera and lens, DX cameras (ie D90, D300/s, Dxxx) will mount both DX and FX lenses. in theory, FX cameras (D700, D3/s) will mount FX lenses only in FX mode (but there are also DX lenses that will work acceptably even in FX format). FX cams will also mount DX lenses but with vignetting on FX mode, will mount ok in DX mode.