This affects BackTrack because it is a Debian issue that occurs here as well.

VirtualBox in general has issues with Debian because of something to do with a problem with headers and/or the kernel, so you have to install dkms first, then VirtualBox 4.2, then you're supposed to be able to install virtualboxguestadditions.iso to enable Drag n Drop and a shared clipboard, as well as shared folders.

However, even once you finally get VirtualBox working in BT5r3 guestadditions still doesn't work. There's not an error message, the features just don't do anything (no Drag n Drop, etc).