I’ve set up aliases to localhost, and corresponding NameVirtualHost settings for Apache, on my Mac for each of the sites I’m developing.  Then I can just enter, for example, “myproject.local” in my browser, and view my work in progress.  (I use the nice Ruby gem “ghost” to manage aliases.)  However, this doesn’t work with a default VirtualBox guest, so below is my method for getting this to work.

Start the VirtualBox VM Manager

1. To begin, start your install of VirtualBox.  I believe that you need at least version 2.2.0, which introduced host-only networking.
   
2. Open the settings for the desired VM and navigate to the Network tab.  You should already have something in the Adapter 1 section.
   

Add a Local-Only Network Interface

1. Click on the Adapter 2 tab.  You should typically see a disabled interface, something like this:
   
2. Enable Adapter 2 by checking the box.  Then change the “Attached to:” box to “Host-only Adapter.”  The Name box shows “vboxnet0″ on my install:
   
3. Save your settings and start your virtual machine.

Verify Host-Only Adapter Address

VirtualBox should create a new network interface on your host OS that is used for host-only networking.  On Mac OS, verify this by entering the following in a Terminal:

ifconfig vboxnet0

You should see something like the following.  Note the IP address – you will need it later:

vboxnet0: flags=8943

Set up Guest OS

You need to set up host aliases in your guest OS that match those you set up in your host, only that you will point them to the IP address you noted previously.  The following instructions apply to Windows XP and newer.

1. Open your hosts file.  Use Start -> Run… and enter “notepad c:WINDOWSsystem32driversetchosts”.  UPDATE: On Windows Vista and Windows 7, there are additional protections on this file.  You will have to run Notepad (or your favorite text editor) as Administrator first – right click on its shortcut and choose “Run as administrator.”
2. Add a line to the file that associates your host-only IP address with your development site aliases.  The IP address comes first, followed by each alias, separated by spaces.

   192.168.56.1    myproject.local otherproject.local

Test the Configuration

As long as your local web server is running on the host OS, you should be able to enter one of your site aliases in the guest’s browser and get the expected results.