If you’ve snagged yourself a copy of Windows 7 Beta 1 and are anxious to give it a whirl, installing it in a virtualized environment is a great way to go. It’s no secret that VirtualBox is my favorite VM application, so I wanted to mention a bit of advice for getting it working properly.

Update: VirtualBox Guest Additions for Windows 7 are now fixed in the 2.1.2 release.

1. If you’ve not yet installed the OS, my first recommendation is to set OS Type to Windows Vista. Although this is largely for display purposes, of all the choices, Windows 7 is the closest in compatibility to Windows Vista.
   

   Select OS Type

2. Go ahead and install Windows just as you would any other: Mount the ISO in the virtual CD/DVD drive and install.
   

   Install Guest Additions

3. Once the VM is finished installing, install VirtualBox Guest Additions. This process might take a few minutes to download, but with enough patience, the ISO will download and mount.
   The problem is, Sun is performing version checking and Windows 7 isn’t yet officially supported. Therefore, when you try to install Guest Additions, you’ll receive the error, “Platform is not supported for Guest Additions yet!”. Here’s the big tip: You must install Guest Additions in compatibility mode.
   

   Guest Additions Error Message

4. To work around this, once the Guest Additions applications pops up, hit Cancel.
   

   Guest Additions Setup Wizard

5. Navigate to Computer (Start Orb?Computer)
   

   Link to Computer

6. Right-click CD Drive (D:) VirtualBox Guest Additions and choose Open.
   

   Explore the Guest Additions CD

7. The “big tip” part:
   1. Right-click VBoxWindowsAdditions-x86 and select Properties.
      

      Guest Addition Properties

   2. When the dialog box opens, switch to the Compatibility tab
   3. Check the box labeled, “Run this program in compatibility mode for”
   4. Select Windows Vista.
      

      Compatibility Settings

8. Hit OK and Run VBoxWindowsAdditions-x86 as normal. The Guest Additions should now install without error and you will be prompted to reboot Windows.
9. After the reboot is complete, you can confirm the installation by verifying that mouse integration works.

Update: Currently, shared folders don’t work, but I’ve posted a workaround.

Best of luck!