Here is a simple guide on how to open ports in ur windows firewall if u r using windows xp service pack 2.
Go to Control Panel in all programs and click on Network and Internet Connections.
Once there click on Network Connections.
This is what u will see.



Right click on the icon which shows CONNECTED and click on properties. (local area connection 2 in my case)

A new window will popup. click on ADVANCED (General is highlighted by default when the window opens) as shown below and then click Settings.



A new window pops up when u click settings as stated above. again select ADVANCED as shown.



Highlight the connection through which u r connected to the internet and click on settings button . In my case it is local area connection 2 .
It will look like this



Click on the ADD button shown above and u get this.



U have 4 places to fill in the above pic.
1- write any name u want for the port.
2- write ur ip. ( to know ur ip, go to start-->run . type cmd and click on ok. it opens the dos mode. type ipconfig and hit enter. note the first ip u get and paste here).
3- choose a port. for e.g. 65355
4- write the same number which u wrote in number 3. i.e 65355.
click on ok .

U have successfully opened one port. to open more ports click on ADD again and open as many ports as u want.
Torrent softwares like bitcomet, new release of abc, azureus etc use one listening port for all downloads, so 1 port should be enuff.
Make sure that u use the same port u opened here in ur torrent client to download stuff
Hope it helps.

Suggestions welcome from every1 to improve the guide.