hi,
I have 2 linux on my machine. red hat and mandrake. i had red hat 8.0 and got this problem with 'input not supported' message when i'm in KDE. but then i installed red hat 9.0 and the message was gone!
so i was happy. but i don't know what was the couse of this problem.
i have mandrake 9.0 and the problem is still here whit this message which flowing on my screen all the time. I'm in the KDE but still... and my buttons on screen doesn't work. i searched the net and find out that something sholud be done in file etc/X11/XF86Config.. i find something someone proposed on the similar problem . but nohting seems to work. sometime when i 'm editing in the file i cannot start xserver anymore so i have to 'upgrade' mandrake (not a problem - 5 minuttes )..
so if anyone outhere has some ides?
thanks.

I've got a 22" ACER AL2223W that had the same problem. Turns out it is XFree86 not knowing the right mode. This is on an ancient RedHat 9 box. I looked in my /var/log/XFree86.0.log and found that it recognized the display and reported a lot of useful data:

(II) R128(0): Supported additional Video Mode:
(II) R128(0): clock: 149.0 MHz Image Size: 474 x 296 mm
(II) R128(0): h_active: 1680 h_sync: 1784 h_sync_end 1960 h_blank_end 2240 h_border: 0
(II) R128(0): v_active: 1050 v_sync: 1053 v_sync_end 1059 v_blanking: 1089 v_border: 0
(II) R128(0): Ranges: V min: 56 V max: 76 Hz, H min: 31 H max: 82 kHz, PixClock max 150 MHz
(II) R128(0): Monitor name: AL2223W
(II) R128(0): ACER

From this, I could construct the horizontal sync and vertical refresh ranges, the display size and the correct mode line for this monitor. I ended up using this section in my XF86Config:

Section "Monitor"
Identifier "Monitor0"
VendorName "ACER"
ModelName "AL2223W"
DisplaySize 474 296
HorizSync 31 - 82
VertRefresh 56 - 76
Option "dpms"
ModeLine "1680x1050" 149 1680 1784 1960 2240 1050 1053 1059 1089
EndSection

That lets it use the LCD's native resolution mode. You can see which numbers I pulled from the log messages to construct all that. I would expect that with different monitors you would need different numbers, but the principle is the same as long as you can get the data out of your X server.

The same section worked in my xorg.conf on a newer Gentoo 2006 distro that had the same "Input not supported" message. But the Xorg server did not give me the same sort of messages, but perhaps Xorg -configure will get the right data for you.

Yes, I know I'm replying to an ancient message, but I pieced this all together with the help of about 30 posts on 10 different forums, so now I'm putting the whole solution out there as a single post so folks can find it easier.