Lubuntu is a lightweight Linux OS that is perfect for emulation because nearly every emulator has a Linux port and the OS uses very little resources. It's also more secure than Mac and is a good Windows alternative. This is how to install it after Windows 7 and use it as a dual boot OS. First you install Lubuntu, choose the install alongside another operating system option when you install Lubuntu and don't use the entire disk or you will overwrite Windows and can't recover it.

Download and burn the Windows 7 recovery disc...

Boot from that disk and choose the command line option.

Type in bootrec.exe /FixMbr then press Enter.

Type in bootrec.exe /FixBoot then press Enter.

Restart the computer.

Once you log on to Windows, download EasyBCD and add an entry for Lubuntu. Select Grub 2 when you create an entry for Lubuntu, then save settings. You can then dual boot both operating systems.
I recommend installing the Ubuntu Software Center after you install Lubuntu with the Synaptic Package Manager, search of the software-center from the package list and mark it for installation, then click on Apply. The Software Center makes it easy to find and install emulators as well as countless other types of software. You should also install Wine, it allows you to run Windows apps on Linux.