To offer remote support you may use the Remote Assistance built in with XP and Vista. In this example an XP PC requested the assistance from a Vista PC.
First, make sure remote assistance is enabled: check the configuration settings and system properties.
Start the ‘Remote Assistance’ programme (Hulp op Afstand). Select ‘Invite someone to help’ (Iemand uitnodigen om te helpen).
This action will send a file (by email) to the person and the pc that will access your pc remotely.
You will need to give the email address of the person that will logon to your pc and define a temporary password (only for one session).
Once the person has received the file with the credentials, he/she can open the file and will be prompted for the password.
Note that the credential file will only be valid for a short while.
If the remote person wants to get control of the pc (Demander le contrôle), then this needs to be granted.
Read more about using Remote Assistance on the Microsoft website