Actually, the best way to try Linux on a Windows system these days is to run it as a VM under Windows. If you are doing this for a friend, colleague or casual acquiantance, it also has the advanatage that you don't have to do anything like repartitioning the disk, that might break Windows or lose their data, and make them very unhappy with you.
Download VMware player (free beer).
Download a ready-to-go trial Linux image, or install the Linux of your choice into a new VM.
I'm assuming that the machine has enough RAM. These days, most do, and many of the rest or older systems are upgradeable for peanuts (which will also make Windows run faster).
There's a significant class of users who won't ever break away from Windows, because they are tied to some piece of Windows-only software by their employer (for example a VPN "solution"), their professional body, their kids' school, their choice of hobby, etc. etc. Running Linux as a VM is superior to dual-boot for anyone in this situation. The other option is running Windows in a VM under Linux.