Configuring xrandr: too small screen size?

[Dotan Cohen]

I have a Dell Inspiron 6400 / 1505E with 1680x1050 built-in LVDS and
external VGA connected to a 1680x1050 LCD monitor. The machine has an
ATI MobileRadeon x1400 graphics card, radeon driver. I can get the
external monitor to mirror the regular display, but I cannot put them
side-by-side with xrandr.

✈dcl:~$ xrandr --output LVDS1 --auto --preferred --output VGA1 --auto
--left-of LVDS1
✈dcl:~$ xrandr --fb 3360x1050
xrandr: screen cannot be larger than 1680x1680 (desired size 3360x1050)
✈dcl:~$ xrandr --fb 1680x2100
xrandr: screen cannot be larger than 1680x1680 (desired size 1680x2100)

The first command has absolutely no effect, that is why I try the
other two. Any ideas what to try next? Thanks!

-- 
Dotan Cohen

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