OK, so this is totally off the cuff...

In a command prompt, cd into wherever you downloaded the file.

Do...
Code:
tar -zxvf 915resolution-0.5.3.tar.gz
This will decompress the archive into a folder.

Now...
Code:
cd 915resolution-0.5.3
make
su
... you will need to stick in your root password here...

Code:
make install
This will compile and install the program.

Now, still being in root...
Code:
915resolution -l
You should see some information e.g.

Code:
Intel 915GM VBIOS Hack : version 0.2

Chipset: 915GM

Mode 30 : 640x480, 8 bits/pixel
Mode 32 : 800x600, 8 bits/pixel
Mode 34 : 1024x768, 8 bits/pixel
Mode 38 : 1280x1024, 8 bits/pixel
Mode 3a : 1600x1200, 8 bits/pixel
Mode 3c : 1920x1440, 8 bits/pixel
Mode 41 : 640x480, 16 bits/pixel
Mode 43 : 800x600, 16 bits/pixel
Mode 45 : 1024x768, 16 bits/pixel
Mode 49 : 1280x1024, 16 bits/pixel
Mode 4b : 1600x1200, 16 bits/pixel
Mode 4d : 1920x1440, 16 bits/pixel
Mode 50 : 640x480, 32 bits/pixel
Mode 52 : 800x600, 32 bits/pixel
Mode 54 : 1024x768, 32 bits/pixel
Mode 58 : 1280x1024, 32 bits/pixel
Mode 5a : 1600x1200, 32 bits/pixel
Mode 5c : 1920x1440, 32 bits/pixel
Mode 60 : 1280x770, 8 bits/pixel
Mode 61 : 1280x770, 16 bits/pixel
Mode 62 : 1280x770, 32 bits/pixel
Mode 63 : 512x771, 8 bits/pixel
Mode 64 : 512x771, 16 bits/pixel
Mode 65 : 512x771, 32 bits/pixel
Pick a mode you don't need (e.g. #38 1280x1024) and overwrite with what you do (e.g. 1280x800)...

Code:
915resolution 38 1280 800
If you need 24 bits per pixel...

Code:
915resolution 38 1280 800 24
You'll need to add this to your Xorg.conf file...

Code:
Section "Screen"
         Identifier  "Screen 1"
         Device      "device"
         Monitor     "LCD"
         DefaultDepth 16

         Subsection "Display"
           Depth       16
           Modes       "1280x800"
         EndSubsection
EndSection
Now start X Windows...

Code:
startx
If it works OK, you'll want to add the 915resolution commands to your startup scripts.

We can work through that later.