Higher screen resolution in VirtualBox?

I've just installed Ubuntu 10.04 into VirtualBox on Windows 7.

Unfortunately the only options showing for screen resolution are 640x480 and 800x600 and the monitor is showing as 'Unknown'.

How would I go about upping the resolution to 1280x1024 (I'm on a 1600x1200 monitor)?

Update
I tried mounting the VirtualBox 'Guest Additions' ISO (from the VBox 'Devices' menu) and doing sudo sh ./VBoxLinuxAdditions-x86.run from the mounted drive, which gave 2 new listed resolutions after a reboot (1024x768 and the 16:9 version of that resolution). These worked when I selected them but disappeared when I switched back to another resolution. I tried rebooting and running VBoxLinuxAdditions-x86.run again but onlu the 2 low res options listed this time.
I think I'm going to reinstall...

Seems to be a VBox problem rather than an Ubuntu problem as after reinstalling 10.4 overwriting the original virtual partition, sudo sh ./VBoxLinuxAdditions-x86.run now has no affect at all.

From ubuntu pelms

• You need to install the VBox guest utilities to add support for the virtualised graphics hardware.

  sudo apt-get install virtualbox-ose-guest-utils virtualbox-ose-guest-x11 virtualbox-ose-guest-dkms
  

  pelms : No luck with that I'm afraid. I still only have the 2 low res options in Monitor Preferences :¬(

  maco : even after reboot?

  pelms : Yep. Even tried this straight after a fresh install of 10.4 (after the updates)
  From maco

• info from lifehacker,

  here is the link http://lifehacker.com/5583650/run-mac-os-x-in-virtualbox-on-windows

  see the comments

  For those who want a custom resolution size:

  First off the res problem is because of VB not the (guest) OS . To fix

  1) open up your (host) OS’s terminal (or cmd in WIndows).

  2) Next navigate to the VB(virtualbox) Folder (ex Windows) Drive(C?):\Program Files\Oracle\VirtualBox. Once there type in the commands;

  VBoxManage setextradata global GUI/MaxGuestResolution any 
  

  (this removes any restrictions in place for the res)

  VBoxManage setextradata "VM name" "CustomVideoMode1″ "Widthxheigthxdepth" 
  

  (VM Name = your VM Name, Widthxheightxdepth would like 1600×900x32 as example aslso that command is all one line not two)

  Your new res should show up. If it doesn’t just try again.

  EDIT:I found other users saying this method works and other methods are suggested like ignoring xorg.conf you should try that (it's the second link) if this method didn't work, i will link them here

  http://ubuntuforums.org/showthread.php?t=634140

  http://ubuntuforums.org/showthread.php?p=5145028#post5145028

  According to the above post the xorg.conf should be editted using

  $ sudo gedit /etc/X11/xorg.conf
  

  and it should contain (after editting)

  Section "InputDevice"
  Identifier "VBoxMouse"
  Driver "vboxmouse"
  Option "CorePointer"
  EndSection
  

  Bananeweizen : Even if this answer might factually be correct (which I don't know), it is hardly readable and therfore will not help that much. Consider using formatting, links and so on.

  pelms : Thanks Siamore. At what point do you press 'F8'? It doesn't do anything once Ubuntu has launched.

  pelms : Why keep marking the guy down..? How many points do you need to be able to edit the post?

  Siamore : @pelms no need to press F8 it should work automatically

  Siamore : @Bananeweizen took your advice i guess tried to say too much and it was my first answer BTW i have -2 but still have 7 rep? how's that?
  From Siamore

• What driver is specified in ur xorg.conf? AFAIK, after installing guest additions the 'vboxvideo' should be used:

  Section "Device"
      Identifier   "Configured Video Device"
      Driver     "vboxvideo"
  EndSection
  

  From Alexey Nedilko

• I can tell you how I do this with Mac OS X as the host system. Maybe it will work on Windows too.

  • I start ubuntu in VirtualBox
  • I open up the terminal on Mac OS X
  • and execute "VBoxManage controlvm [name] setvideomodehint 1280 1024 24" (replace [name] with the name of your ubuntu vm)
  From

• Once the Vbox Additions has been instaled (and reboot the guest os), press Host + H, then maximise the window, thats sould do the trick..
  If not, maybe you are using an old version of vbox (therefore, the Vbox Additions might has an incompatibility..)

  From Axel