xrandr dual head configuration: how-to required

[Hiisi]

Hi, list!
Recently I installed F15-rc1 on my computer. The machine is AMD Phenom
with 2 GB of RAM. It has two graphics adapters - one internal,
integrated into motherboard and the other is PCI-express card. Here's
the link to motherboard manufacturer specifications:
http://www.msi.com/product/mb/740GM-P25.html#?div=Detail
PCI-E card is Redwood [Radeon HD 5670].
The machine has two monitors. One attached to PCI-E card is 21.5 BENQ GL2240:
http://www.benq.com/products/product_detail.cfm?product=1765
The other one connected to internal video-out is NEC LCD 72VM.
I'm trying to configure dual-head. Last time I did it I used Xorg.conf.
In BIOS under 'Advanced BIOS Features I have' following options:
1. Primary Graphic's Adapter: Internal
                                            PCI
                                            PCI-E
2. On-Chip VGA                     Enabled
3. Surround View (If PCIE is Primary display, allow INTGFX to be
secondary display) Disabled

If I choose 'Internal' in option 1 NEC-monitor is used by default and
BENQ couldn't start (it does not detects in display configuration
menu). On the other hand, if I choose PCI or PCI-E NEC goes to sleep
mode.
I saw in google that now one should use xrandr to configure dual
screen. Could anybody provide me instructions on how to achieve that?
TIA
PS. Additional info:
xrandr command output when NEC is used as primary monitor:
Screen 0: minimum 320 x 200, current 1280 x 1024, maximum 8192 x 8192
VGA-0 connected 1280x1024+0+0 (normal left inverted right x axis y
axis) 338mm x 270mm
   1280x1024      60.0*+   75.0
   1152x864       75.0
   1024x768       75.1     70.1     60.0
   832x624        74.6
   800x600        72.2     75.0     60.3     56.2
   640x480        72.8     75.0     66.7     60.0
   720x400        70.1
DVI-0 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
xrandr output when BENQ is used as primary:
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
HDMI-0 disconnected (normal left inverted right x axis y axis)
DVI-0 disconnected (normal left inverted right x axis y axis)
VGA-0 connected 1920x1080+0+0 (normal left inverted right x axis y
axis) 477mm x 268mm
   1920x1080      60.0*+
   1680x1050      60.0
   1600x900       60.0
   1280x1024      75.0     60.0
   1280x960       60.0
   1280x800       59.8
   1152x864       75.0
   1280x720       60.0
   1024x768       75.1     60.0
   1024x576       60.0
   832x624        74.6
   800x600        75.0     60.3
   640x480        75.0     60.0
   720x400        70.1
$ glxinfo | grep -i "\(render\|opengl\)"
direct rendering: Yes
OpenGL vendor string: X.Org
OpenGL renderer string: Gallium 0.4 on AMD REDWOOD
OpenGL version string: 2.1 Mesa 7.11-devel
OpenGL shading language version string: 1.20
OpenGL extensions:
    GL_NV_conditional_render, GL_AMD_draw_buffers_blend,
-- 
Hiisi.
Registered Linux User #487982. Be counted at: http://counter.li.org/
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