Choose “Mac OS X Extended (Journaled)” and name the hard drive something, then click on “Erase”.Select the name of the virtual hard drive on the left side menu of Disk Utility (15GB VBOX HARDDRIVE or something similar) and then click on the “Erase” tab.
Pull down the “Utilities” menu and select “Disk Utility” – this next step is important because without it the virtual drive will not appear in the install menu.Now boot the newly created VM by clicking on “Start” and let the Snow Leopard installer load, click through to the “Install Mac OS X” screen.Confirm the specs, boot disk of and choose “Create”.Select the Snow Leopard DVD, DMG, or ISO as the primary boot drive.Choose “Mac OS X” and “Mac OS X Server” as the OS and OS Type.