Like almost all Linux desktops, Mint is free and it can run on almost any PC you have at hand. All it requires is an x86 processor; 512 MBs of RAM (you’ll be happier though with 1GB); 5 GBs of disk space; a graphics card that can handle 800×600 resolution; and a DVD drive or USB port. That’s all.
I’ve been using Ubuntu for about 6 weeks now. It’s good for what I need. I’m no expert with it yet, but I’m getting it figured out.