This will depend on which Windows OS and versions are running on the various machines. If using Win7 Pro and up on all machines, you don't need to buy anything. Remote desktop, as I recall, was introduced with XP but the client had to be XP Pro.
I am wondering if there is any software or built in features for windows 7 to allow me to remotely connect to a PC over the internet, WITHOUT installing additional software on the client PC. Any help is appreciated, program may be free or paid it does not matter I simply need software or a way to do this without installing additional components on the client PC. Thank you in advanced!