How to Access Host's Shared Folder from MacOSX Guest
While Guest Addition is not yet available for Mac OS X guest in VirtualBox, we cannot access VirtualBox's shared folder from our Mac OS X guide as in guests like Windows. To access the files on our host machine, we need to SMB (Server Message Block) protocol.
Well, there is no need for us to understand the details of SMB. Simply do the followings to allow file sharing between the host machine and the guest:
- On your host machine, create and configure your share.
- For Windows host, the share can already be already via SMB protocol.
- For Mac OS X host, we have to enable "Share files and folders using SMB (Windows)" on our user account.

- To access the share from the guest VM, click "Connect to Server..." in the Finder menu bar (you can gain access to the Finder by first clicking on the Mac OS X desktop).
- Enter smb://10.0.2.2 in the "Server Address" field and click "Connect".
- You will be prompted for the user name and password. Enter the user name and password that are required to access your host's share folder.
- For Windows host, you can use your Windows host machine's username and password.

- For Windows host, you can use your Windows host machine's username and password.
- After connecting to the host machine, a list of shared folders available will be displayed. Simply choose the one that you wanted and click "OK".

Done!
I think the only issue that you want to ask is "why the server address is 10.0.2.2?". Well, if you take a look at the Network settings in your Mac OS X guest, you will see that "10.0.2.2" is the Router. This is actually your host machine from your guest VM's point of view!
If you want to, you can actually replace it by the real IP of the machine that you want to access.