Is it possible to set up framebuffer and have 1680x1050 as screen resolution? How can I do this? (I'm using grub)

I think that when using a framebuffer, you're dependent on your BIOS to correctly list available resolutions. If your BIOS doesn't list your resoultion, there are some tools that will allow you modify the RAM image of your BIOS in order to add this resolution. If you're using an i855 chipset, try i855resolution (search in google). I used it successfully to get 1400x1050 on a Dell laptop with a buggy BIOS.

Could you explain how you got this resolution and post your config? I have a Dell D800 laptop.

I don't have this Laptop at hand right now, as it's my mother's laptop...

I have looked for D800 linux reviews here :

http://www.linux-on-laptops.com/dell.html

it looks like the D800 comes with a NVidia card. Can you confirm that ?
to make sure, do :

If you have a NVidia card, that's very good because you can install the nvidia driver and it will easily handle whatever resolution you want.

If you have a i855 chipset, look for i855wrap and i855resolution in google, I'm sure you'll find what you need. You'll have to use the i810 driver in your X11 config file, and you'll need to add a few lines to call i855resolution and i855wrap at startup with proper arguments.

I you really can't work it out, tell me and I'll look at what I had precisely done on my mother's laptop...

Well, probably you will also be able to use fbdev instead of i810, I don't know, never tried.

sorry, the tools are called 855wrap and 855resolution, without an 'i'.