Step by step guide:

• Create a host machine folder to share to the guest machine for example in my case - D:\shared2guest
• Add the folder to the shared folder properties of the Linux guest virtual machine and named it as shared2guest
• Create a folder at /home/username/shared2guest to be the mount point of the VirtualBox shared folder in the Linux guest
• So, for the Linux guest in VirtualBox, the command to use the shared folder is " mount -t vboxsf [shared folder name] [mount point]"
• The command I was using is : " mount -t vboxsf shared2guest /home/noor/shared2guest"

I am by the way, logged on as the root and my linux guest is CentOS 5.4. In other case where you are not, refer to this.

Love,