I found some topics about dualbooting, but nothing was exactly what I need, so: I have Win7 and I installed Ubuntu 12.04 LTS from a flash drive. Everything went smoothly and I was given the "for installation to finish, need to reboot" screen. I removed the flash drive, the PC restarted. I was expecting to be greeted with the menu where I choose the OS I want to launch, but instead the Windows happily starts.