VPN app/VPN macbook 2003 10.6.8
You do not say which 2003 model of Mac you have but 2003 Macs do not have Intel processors and your version of macOS (normally referred to as Snow Leopard) is old and likely unsupported by most current applications both for the OS version and the PowerPC chip in your Mac.

macOS does have a built-in VPN (I believe with Snow Leopard as well...). PPTP is fairly common (especially if it is a Cisco or Cisco-compatible VPN) and you might be able to configure it to work with your VPN service, but I would not count on it, especially if it is a commercial VPN service, as they often use their own APP to connect to their VPN service.

You are possibly out of luck, unless someone here knows specifically one that works with your configuration.

If you indicate what you are trying to accomplish or even which ones you wanted to try that might help us help you.