To do a dualboot, first install the windows OS of your choice on the computer, then on windows download an .ISO file of the linux distribution that you want. Personally I would recommend Xubuntu, it uses a better desktop environment than Ubuntu and also doesn't have that shitty Amazon search tracking (
You must login or register to view this content.) The next step is to download Universal USB Installer or any one of the other programs that can make a Live USB for you, install it and plug a USB flash drive into the computer. Run the USB installer and select your USB flash drive, locate the ISO file and tell it to install that on the USB, once that's done. Turn your PC off, with the USB plugged in and pray it boots from the USB first time, if not then you'll need to press F10 repeatedly after turning on your PC to get into the BIOS settings menu, whilst in there you should change the boot order to allow USB to boot first, you may also have to turn off secure boot too if it still fails to boot. So now when you turn on the PC it should boot from the USB, and a Xubuntu logo will show up, follow the instructions give to you and install it along side windows 7 / 8 whatever you use once the install completes, remove the USB and start it again, you'll then be presented with a GRUB menu on boot that will let you choose what OS to boot into. Finished.