Another great tip from Lifehacker.com:

You can quickly change the size of the Firefox window by clicking a bookmarklet. Reader Domen writes in and explains how to set up the bookmarklet, which is perfect for users with extra screen estate. Create an empty bookmark in your Bookmarks Toolbar and enter the following as the location:

javascript:window.resizeTo(1280,1050);

Edit: Well, I was going to be nice and post pre-made bookmarklets for you, but WordPress strips any JavaScript links of their magic. :-P

Éste wallpaper es de temá bélico...

Firstly, power down the image and edit the configuration options for your image, click on the "Video options". Check 'Enable custom screen resolutions' and add the resolution (in this case, 1280x800). Make sure the resolution is enabled (checked). See the screenshot below for an example of what it should look like:

Next, boot into the VM image and let's take a look at the xorg.conf file, here are the lines I changed that actually matter:

#HorizSync 31.5 - 48.5
HorizSync 30.0 - 82.0
#VertRefresh 50.0 - 90.0
VertRefresh 50.0 - 90.0
#Option "DPMS"
ModeLine "1280x800" 80.58 1280 1344 1480 1680 800 801 804 827 -HSync -VSync

These should be in the section right after 'Section "Monitor"'. After changing the hsync and vsync as well as adding the mode, I changed the display section from:

SubSection "Display"
Depth 24
Modes "1024x768" "800x600" "640x480"
to:
SubSection "Display"
Depth 24
Modes "1280x800" "1024x768" "800x600" "640x480"

It's a good idea to change the modes for each of the depths (at least 8, 15, 16 and 24) also.

After rebooting (or killing X with Ctrl+Alt+Backspace), your screen should come up in 1280x800 resolution. Hurray!

You can see an example of my desktop setup for Hex 1.0.3-RC2 here:

You can get a copy of my entire xorg.conf file here. (Note that in this xorg.conf, CapsLock is remapped to additional control because I hate capslock with a passion).

Hope this helps someone out there :)