To clarify the title of this post, I am running the latest Virtualbox (3.2.6) on a Windows 7 host with a linux (Kubuntu) guest. I am using the guest as a development box for a website I am working on and would like to access it from Win7 to test with Internet Explorer (yuck). This is something I've been wanting to get to work for a while but never really looked into it. Today I decided to break down and investigate. Turns out it is a fairly simple process.
Option 1 - Port Forwarding
I first found this blog post that discusses setting up the proper port settings for Virtualbox. I tried this and ran into some errors, including the one from the first comment. Just copying and pasting from the site I started up VB and immediately got the errors. I realized this is because I am using one of the Intel network adapters, not PCNet as in the example. The secret here is figuring out the appropriate device name to use in the paths given by the post. The way I found these was to look at the VBox.log file for the appropriate machine. In it you will find many lines, but you're looking for level 2 devices that look something like this:
[/Devices/i8254/] (level 2)
In this case it is the device for the Intel network adapters. So, adjusting the code from the blog, you would run each of these at the command prompt...
VBoxManage setextradata YourGuestName "VBoxInternal/Devices/i8254/0/LUN#0/Config/apache/HostPort" 8888 VBoxManage setextradata YourGuestName "VBoxInternal/Devices/i8254/0/LUN#0/Config/apache/GuestPort" 80 VBoxManage setextradata YourGuestName "VBoxInternal/Devices/i8254/0/LUN#0/Config/apache/Protocol" TCPShutdown
One thing to be careful of here is the already mentioned errors. These will prevent you from starting up the VM at all. The most common error is verr_pdm_device_not_found, which stems from having the incorrect device for the current settings, so using pcnet in the above code but having and Intel adapter chosen in the settings, or having an incorrect name in the path, say you missed the 'i' in i8254. The way to fix this is close out of VirtualBox--VMs and the program itself--and edit the xml configuration file for the machine. It will have <ExtraDataItem> entries near the top to correspond to the settings you changed above. Delete these three lines, startup VB, and your VM should now be able to start itself.
The blog goes on to say you should then use localhost:8888 to access the web server but I never got this to work. I admit I did not try very hard, so the solution here could be a simple fix. I'm guessing it is some issue with Windows 7 networking handling the localhost, which is not something I felt like messing with, so I found a different solution.
Option 2 - Bridged Adapter
The network settings on my guest were to set it to connect via NAT. Changing to bridged, I was then able to browse to the guest's IP in my host (192.168.1.5 in this case) and everything worked fine. Much simpler and no messing with VBoxManage.
Option 3 - Host-only Adapter
The Host-only Adpater will also work but it will not give outside internet access to your guest. The plus side is that no physical network device is required, but for me it is hard to imagine a computer without a network device in this day and age.
Overall Option 2 is the best as I see it: simple and effective.