I have installed Linux Fedora, Ubuntu and Linux Mint 8,9,10 as guests in Virtualbox with Windows 7 as host numerous times without problem. I am interested to try LMDE since I like the idea of a rolling distro rather than reinstalling/upgrading every six months. So, I downloaded the LMDE iso and installed it as a guest in Virtualbox. I found it somewhat tricky to figure out the right magic phrase to get the guest additions to install so I thought I would put this note here in case anyone else was new to debian and trying to figure this out. First, update your LMDE system and then click on Devices in the Virtualbox menu in the upper right hand corner and select VboxGuestAdditions.iso under CD/DVD devices.
Then when the cd image for Guest additions is mounted in the LMDE guest, open a terminal and switch to su (rather than sudo) and once you are root you use sh. So, click to open the CD image and drag the correct VboxGuest additions onto a command line that starts with sh and then hit enter. The guest additions will install correctly.
I hope this helps someone since I just wasted an hour using trial and error.