i have a usb modem internet connection , and my dad have a cable internet connection.i want to access remote desktop activity from my end.how i establish this connection.plz send me with example both of them.You can access the desktop of those remote computers using either Microsoft or third party software. I've been told the third party software is easier to setup and use (but have not experience with them). I cannot and will not provide step-by-step instructions for any of these. PERHAPS someone else will volunteer.

Microsoft provides two different functions: Remote Assistance and Remote Desktop. You should look them up using the "Help and Support" function within Windows XP. The Microsoft software requires port 3389 to be open on the firewall.

Remote assistance allows you to connect to an already established Windows logon session to demonstrate, assist, or fix an issue in FULL view of the user. They can see everything you do, disconnect you at any TIME, and MUST invite you to assist before you can connect.
Remote Assistance in Windows XP
Step-by-Step Guide to Remote Assistance

Remote desktop permits you to logon to a remote desktop that is powered on and booted up with Windows (but not necessarily logged into a user account). If a user is logged on when you try to connect, you can force them to log out but you cannot both be on at the same time.
Get started using Remote Desktop with Windows XP Professional

Enabling Remote Desktop in Windows Vista
Enabling Remote Desktop in Windows XP
Remote Desktop Connection from Internet

If you want secure communications, I believe you need to use a Virtual Private Network (VPN) connection. This is something I haven't done yet.
Virtual Private Network (VPN) Introduction

There are numerous third party solutions. Here are some that are either free or free for non commercial use:
https://secure.logmein.com/US/home.aspx
LogMeIn Free
LogMeIn Hamachi2 (VPN)

CrossLoop 2.51
RealVNC 4.1.3
TightVNC 1.3.10
UltraVNC 1.0.6.5