If your using virtual box its very nice to have the guest additions installed on your vbox system. It changes the vbox systems resolution according to its window size, copy and paste from vbox to main system and you don’t need to push an control button to leave the vbox system. Another nice feature is the time synchronization and the shared folder.
Vbox Guest Additions doesn’t run out of the box at your lenny installation. There is a debian package available, but if your using a newer virtual box version this package will not bring you all features.
So first you need to mount the Vbox Guest Additions image.
Devices → CD/DVD Devices → VboxGuestAdditions.iso
After this open the terminal in your vbox and become root. You have to install the linux-header and the linux-source files. With these packages several other programs like gcc and make will be installed.
~$ aptitude install linux-headers-YOURKERNEL
~$ aptitude install linux-source-YOURKERNEL
~$ sh /media/cdrom/VBoxLinuxAdditions-YOUR_SYSTEM.run
If you don’t know YOURKERNEL use
~$ uname -r
YOUR_SYSTEM is x86 for 32bit debian and amd64 for 64bit debian.