To install guest additions in your newly installed Linux Mint 10, go to CD folder. It might have a bit strange name. Mine mounted here:
cd /media/VBOXADDITIONS_4.0.8_71778
I wish Linux would not have the typical Windows disease but sometimes it shows some symptoms. It freezes! And than you just have to kill the program. Luckily it is even easier than ctrl-alt-del. You can have designated icon on the panel.