How to share files in Sun Virtual Box ?

Shared folders allow you to access files of your host system from within the guest system, much like ordinary shares on Windows networks Sharing folders in Microsoft virtual PC is much simpler than in virtual Box. Just adding the shared folder will add a new mapped icon in "my computer" to provide access to host files

This is not the case in Virtual box, sharing is accomplished using a special service on the host and a file system driver for the guest, both of which are provided by VirtualBox.To share a host folder with a virtual machine in Virtual Box, you must specify the path of that folder and choose for it a "share name" that the guest can use to access it.

After this step I'm expecting a new drive in "My Computer" as a typical Microsoft Virtual PC user. But there is no new drive. After digging into the help files, Virtual Box requires a explicit "net use" command to mount that shared drive.

net use x: \\vboxsvr\sharename

vboxsvr is a fixed name(might be helper service which runs on the guest along with Guest additions), "sharename" is the alias name which is provided while mapping the host drive

Virtual machine guest additions installation is a pre-requisite for folder sharing

How to compact Virtual hard drives?

When we develop in our virtualized dev environment, the virtual hard disk will expand dynamically in size. The problem is they don't compact automatically when we clean-up the VHD's. steps to reduce the VHD in size

1. Remove all unwanted files in temp locations or use CCleaner to remove all unwanted files.
2. Uninstall all programs which are unused in the dev environment.
3. Defrag the disk by using the system defragmenter.
4. select Capture ISO Image from CD menu and browse to the Virtual PC additions
directory
5. Location is %ProgramFiles%\Microsoft Virtual PC\Virtual Machine Additions by default.
6. Mount Virtual Disk Precompactor.iso. The precompactor will start automatically.
7. Once it's done , shut down the Virtual Hard disk.
8. Select the VPC from the Virtual PC console. Click on the settings button and select the Harddisk1 from the left pane.
9. Click over the "Virtual Disk Wizard" button and click next in the wizard.
10. select Edit existing disk, next choose the compact option - this can take a while to complete

For more info KB888760 How to prepare a Virtual Server 2005 virtual hard disk file to send to Microsoft Product Support Services