Here is how it goes.
Insert 6.10 live cd, screen ok, select keyboard, safe graphics, 1024x768x16; boot goes on till screen becomes black, with quick flashes. Open console with ctrl-alt-f1. 

lspci -n
00:00.0 0600: 8086:2778
00:1c.0 0604: 8086:27d0 (rev 01)
00:1c.4 0604: 8086:27e0 (rev 01)
00:1c.5 0604: 8086:27e2 (rev 01)
00:1d.0 0c03: 8086:27c8 (rev 01)
00:1d.1 0c03: 8086:27c9 (rev 01)
00:1d.2 0c03: 8086:27ca (rev 01)
00:1d.3 0c03: 8086:27cb (rev 01)
00:1d.7 0c03: 8086:27cc (rev 01)
00:1e.0 0604: 8086:244e (rev e1)
00:1f.0 0601: 8086:27b8 (rev 01)
00:1f.1 0101: 8086:27df (rev 01)
00:1f.2 0101: 8086:27c0 (rev 01)
00:1f.3 0c05: 8086:27da (rev 01)
03:00.0 0200: 8086:108b (rev 03)
04:04.0 0300: 1002:515e (rev 02)
04:05.0 0200: 8086:1076 (rev 05)

discover
ES1000 (RN50)	XFree86	ati	1002515e

xresprobe ati
id: L15C
res: 1024x768 832x624 800x600 720x400 640x480
freq: 31-60 56-75
disptype: crt

xorg.conf
# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the /etc/X11/xorg.conf manual page.
# (Type "man /etc/X11/xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "Files"
	FontPath	"/usr/share/X11/fonts/misc"
	FontPath	"/usr/share/X11/fonts/cyrillic"
	FontPath	"/usr/share/X11/fonts/100dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/75dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/Type1"
	FontPath	"/usr/share/X11/fonts/100dpi"
	FontPath	"/usr/share/X11/fonts/75dpi"
	FontPath	"/usr/share/fonts/X11/misc"
	# path to defoma fonts
	FontPath	"/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
	Load	"i2c"
	Load	"bitmap"
	Load	"ddc"
	Load	"dri"
	Load	"extmod"
	Load	"freetype"
	Load	"glx"
	Load	"int10"
	Load	"type1"
	Load	"vbe"
EndSection

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"CoreKeyboard"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"pc105"
	Option		"XkbLayout"	"it"
	Option		"XkbOptions"	"lv3:ralt_switch"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
	Option		"CorePointer"
	Option		"Device"		"/dev/input/mice"
	Option		"Protocol"		"ExplorerPS/2"
	Option		"ZAxisMapping"		"4 5"
	Option		"Emulate3Buttons"	"true"
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "stylus"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "stylus"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "eraser"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "eraser"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "cursor"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "cursor"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "Device"
	Identifier	"ATI Technologies, Inc. ES1000 (RN50)"
	Driver		"ati"
	BusID		"PCI:4:4:0"
EndSection

Section "Monitor"
	Identifier	"L15C"
	Option		"DPMS"
EndSection

Section "Screen"
	Identifier	"Default Screen"
	Device		"ATI Technologies, Inc. ES1000 (RN50)"
	Monitor		"L15C"
	DefaultDepth	24
	SubSection "Display"
		Depth		1
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		4
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		8
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		15
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		16
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
	SubSection "Display"
		Depth		24
		Modes		"1024x768" "832x624" "800x600" "720x400" "640x480"
	EndSubSection
EndSection

Section "ServerLayout"
	Identifier	"Default Layout"
	Screen		"Default Screen"
	InputDevice	"Generic Keyboard"
	InputDevice	"Configured Mouse"
	InputDevice     "stylus" "SendCoreEvents"
	InputDevice     "cursor" "SendCoreEvents"
	InputDevice     "eraser" "SendCoreEvents"
EndSection

Section "DRI"
	Mode	0666
EndSection


***issue was solved changing driver from "ati" to "vesa" in section "device" of xorg.conf


thanks for your support,
regards,
GianLuca