Remote Access for Windows XP and Vista

I have a laptop that I'm bringing with me every time I go to school. And I also have a desktop in my home, my problem was I cannot access my desktop using my laptop although my telnet was enable all configuration for remote access was enabled. I try connecting through dynamic IP and the IP that my ISP provide. I don't know what IP Address i need to connect with my desktop computer.? Please help me. by the way the OS of my laptop was Vista and my desktop was XP
