I currently run Windows 7 and Ubuntu 12.04 as a dual-boot system. I need Linux, but Ubuntu freezes at least once a day. So I want to replace it with another distribution like Debian or LMDE. On the other hand I am a little concerned that I'll have troubles working with a less user friendly operating system than Ubuntu. So would it be possible to just scale down the Windows partition and install the next Linux as a third system? Thus, with a "triple-boot system" I could keep Ubuntu until I feel familiar with the new system. Afterwards, I guess, it should be possible to replace the Ubuntu partition by expanding the new system?
In a word, YES. GRUB and GRUB2 accommodate multiple OS. http://www.pagestart.com/win7heptaboot01.html has more info, as does https://askubuntu.com/questions/351002/triple-boot-ubuntu-windows-showing-up-but-not-red-hat