I was having trouble viewing a shared folder from the host operating system (Mac OSX in my case) on the guest operating system (Vista). Here’s how to make it happen.
Firstly, create a shared folder on your OSX machine (right-click on the folder you want to share/see in Vista choose ‘Get Info’ from the menu and then tick ‘Shared Folder’)
Now start your guest machine (Vista in this instance) and choose Devices from the VirtualBox top bar menu.
Choose ‘Shared Folders…’ and click the plus button on the right of the resultant window and browse to the shared folder you just made. I added this under both Transient and Machine folders.
Now in Vista, open Computer from the start menu and click the ‘Map network drive’ button.
Now for the bit none of the documentation tells you! Choose a drive letter for the shared drive but instead of browsing for the drive (as you would normally) you need to enter this in the folder field: \\vboxsvr\YOUR SHARED FOLDER NAME
Obviously you need to replace YOUR SHARED FOLDER NAME with whatever the name of your shared folder is, in my case the entry looked like this: \\vboxsvr\Virtual_Shared
Then just click return and the drive should show. 🙂