Doesn't look like you can.  The XF86Config(5) file says:

    DISPLAY SUBSECTION

    [...]

    Depth depth
	  This entry specifies what colour depth the Display subsection is
	  to be used for.  This entry is usually specified, but it may  be
	  omitted to create a match-all Display subsection or when wishing
	  to match only against the FbBpp parameter.  The range  of  depth
	  values that are allowed depends on the driver.  Most driver sup-
	  port 8, 15, 16 and 24.  Some also support 1 and/or 4,  and  some
	  may  support other values (like 30).  Note: depth means the num-
	  ber of bits in a pixel that are actually used to  determine  the
	  pixel  colour.   32  is  not a valid depth value.  Most hardware
	  that uses 32 bits per pixel only uses 24 of  them  to  hold  the
	  colour information, which means that the colour depth is 24, not
	  32.


You could try to experiment and change your XF86Config to look
something like the following; YMMV:

    Section "Screen"
	    Identifier "Screen[0]"
	    Device     "..."
	    Monitor    "..."
	    DefaultDepth     32
	    SubSection "Display"
		    Viewport   0 0
		    Depth     32
	    EndSubSection
    EndSection

Brian.


On 2007.09.25 07:38:23 -0400, Nguyen, Son N. wrote:
> How can I set to 32-bit color quality display with xf86config?
> Thanks.
> 
> sn

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli
Brian.



On 2007.09.25 07:38:23 -0400, Nguyen, Son N. wrote:
> How can I set to 32-bit color quality display with xf86config?
> Thanks.
> 
> sn

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli
On 2007.09.25 07:38:23 -0400, Nguyen, Son N. wrote:
> How can I set to 32-bit color quality display with xf86config?
> Thanks.
> 
> sn

-- 
  Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
      "Amusement to an observing mind is study." - Benjamin Disraeli