I have an Inspiron 1100 that I installed LM12 on (over Ubuntu 10).
The resolution was a perfect native 1024x768 in Ububtu. Now, I have the same problem listed in this thread.
The display shows up now in the middle of the screen (previously it was in the top left with a "ghost" below it, and black to the right of both.
Now I get blue vertical lines through the whole screen, and still only 640x480 or so. The display section of System Settings is locked at 640x480 and sometimes it's "laptop" other times, "unidentified" or "unknown."
I've modded this several times now according to posts in this forum. Here's what I had to do to get it to work:
Install startup-manager (not included in Mint 12) using Software Manager. Applications>Other>Software Manager
Once installed, it shows up in the same menu: Applications>Other>Startup-Manager
Select 1024x768 on both tabs of Startup-Manager, close it.
Open etc/default/grub, as administrator (right-click on grub to select Open As Administrator) and change the line where vga=791 to vga=792, per tjwells in this thread.
Then open Software Manager again and download and install Intel-Microcode as well as microcode.ctl (search for both and install).
After completing all of this, reboot your computer.
That's it. It should work. The microcode steps may or may not be necessary. I did it and it works, but I did a lot of things before it worked.
All of this is just a combination of three threads on this subject. In sum, it worked for me.
Best of luck to anyone else out there with an old DELL.