I'm now the happy owner of a Dell 2005FPW, which is a 20.1" wide aspect LCD panel, with a maximum resolution of 1680 x 1050.
Unfortunately I am also the proud owner of a video card which uses the Intel 855 chipset. It's a notorious pain. I don't know how it compares to other video cards, since it's the only modern one I've had in quite a while, but I can say that it definitely causes me grief.
In the end, though, I was able to get to the monitor's maximum resolution in Xorg. It wasn't easy, and I only got there with help on #xorg from a developer.
I'm sorry this write-up isn't prettier, but it's the best I have time for, and some contribution is better than none.
The first thing I did when I got the monitor was Google for some appropriate Xorg modelines. I found a lot of variations. I tried them all out in the config, and, from studying the log file, could see that Xorg was initially recognizing the resolution, but later on, it was being rejected by the i810 driver. The errors looked something like,
(II) I810(0): Not using mode "1680x1050" (no mode of this name)
I tried 855resolution, but that didn't do it for me.
Some example modelines I tried, both from the Web and from running gtf:
Modeline "1680x1050" 147.14 1680 1784 1968 2256 1050 1051 1054 1087 Modeline "1680x1050" 147.14 1680 1784 1968 2256 1050 1051 1054 1087 -HSync +Vsync Modeline "1680x1050_60.0" 146.2 1680 1784 1960 2240 1050 1053 1059 1089 -HSync +Vsync Modeline "1680x1050" 146.2 1680 1784 1960 2240 1050 1053 1059 1089 -HSync +Vsync ModeLine "1680x1050" 146.2 1680 1960 2136 2240 1050 1080 1086 1089 -hsync +vsync Modeline "1680x1050" 154.20 1680 1712 2296 2328 1050 1071 1081 1103 Modeline "1680x1050_60.00" 147.14 1680 1784 1968 2256 1050 1051 1054 1087 -HSync +Vsync
This turned out to be the winner:
Modeline "1680x1050" 146.2 1680 1784 1960 2240 1050 1053 1059 1089 -HSync +Vsync
I don't know if it's the best one or not, but I know that it is part of my currently working setup, so I'm not going to change it unless I hear good reason to.
The rates I'm using are:
HorizSync 30.0 - 83.0 VertRefresh 56.0 - 75.0
Also include these items in the Device section for your 855 card:
VideoRam 131072 Option "NoDDC" Option "ForceBIOS" "1600x1200=1680x1050"
Never heard of "ForceBIOS"? No, me neither. To use it, you'll need to download the testing version of the i810 driver and drop that in your X11 modules directory, replacing your current i810 driver (I copied the old one to another location just in case). A reboot may be necessary.
I think the value of VideoRam I have is right for me, I pulled it from lspci -vv.
So, there are my disorganized tips. If you're working on this problem but not having any luck, give me a shout and I'll try to remember more about what I did. I imagine there will be a few people out there working on these now, since they're basically on a fire sale over at Dell.