I came to know that a dailer connects to internet through very expensive numbers without user persmission.

How can I know that my computer is not dailed through one of them.

I use dsl modem and have windows xp.

If you think you have malware on your computer, use the programs below. Let us know what they find. DSL does not use a dialup connection but you still could have the malware on your computer.

Install Super Antispyware. Run it in safe mode. Allow it to quarantine whatever it finds.
http://www.superantispyware.com/

Run the online scan for Bit Defender in normal mode. Allow it to quarantine whatever it finds.
http://www.bitdefender.com/scan8/ie.html

How to Start Windows in Safe Mode:
http://www.bleepingcomputer.com/tutorials/tutorial61.html