How can I configure my ADSL modem and Home PC to be able to access from external?
Solution 1:
To expand on the answer by TheTXI
Using a service like DynDNS you create a new account which will provide you with a unqiue Url, for example myhome.dyndns.org.
Depending on whether you have an ADSL Router or Modem the process differs slightly. When using an ADSL router you need to configure the Dynamic IP settings on the router to point to your new DynDNS URL using the username and password you supplied. This will ensure that every time the line resets the new IP is given to DynDNS. This process normally takes about 20 minutes. If your using an ADSL Modem you will need to download seperate software to do this.
When using an ADSL router you also need to setup Port Forwarding. This will allow the router to send data for a particular port, either VNC or RDP to your machine. To use this I recommend either giving the machine you want to connect to a Static IP directly or using DHCP assigned static IP based on Mac address.
Solution 2:
You can do this using
DynDNS (will take care of the dynamic IP problem by always updating with the new IP when it is given)
RealVNC (used for the remote desktop connection)
You could also use other software products to achieve the same results, but this is typically the most popular combo.