For fun, not thinking something like this would exist, I looked up 'boot Linux and windows simultaneously' and after a while I found andLinux. It's not a real simultaneous boot, but it has the same functionality:

andLinux is a complete Ubuntu Linux system running seamlessly in Windows 2000 based systems (2000, XP, 2003, Vista, 7; 32-bit versions only). This project was started for Dynamism for the GP2X community, but its userbase far exceeds its original design. andLinux is free and will remain so, but donations are greatly needed.

andLinux uses coLinux as its core which is confusing for many people. coLinux is a port of the Linux kernel to Windows. Although this technology is a bit like running Linux in a virtual machine, coLinux differs itself by being more of a merger of Windows and the Linux kernel and not an emulated PC, making it more efficient. Xming is used as X server and PulseAudio as sound server.

andLinux is not just for development and runs almost all Linux applications without modification.

>> Requirements:

OS: Windows 2000 / XP / 2003 / Vista / 7 (currently only the 32-bit versions are supported)
Memory: at least 128 MB (192 MB or more is recommended)
Note that you should have enough memory left for Windows (at least 128 MB for Windows 2000 / XP / 2003; at least 512 MB for Windows Vista / 7)!
Hard disk space: 2.5 GB (XFCE version) / 4.5 GB (KDE version)
Note that you need an NTFS file system (which is default since Windows 2000) because you can't create files larger than 2 GB on FAT(32) file systems!
A good internet connection (to be able to install further applications via apt-get / Synaptic)
Some basic Linux skills to proceed once andLinux is installed

>> Download:

KDE version (500mb) @Sourceforge

XFCE version (200mb) @Sourceforge

>> Official Homepage:

Klick me!

>> I have some startup problems, the local boot scripts are not loaded correctly so I only have an emulated terminal. Let's see if I get it fixed. This program is surely not a thing for Linux newbies or Windows only user...