Problem with email function

Hi im using drupal 5.2 and whenever i register new user i get this Warning and i really dont know how to figure this out

warning: mail() [function.mail]: "sendmail_from" not set in php.ini or custom "From:" header missing in C:\xampp\htdocs\drupal1\includes\common.inc on line 1991.

please guide me how to get rid of this problem

and in drupal 6.2 im getting this error again while registering a new user with an email address

* warning: mail() [function.mail]: Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set() in C:\xampp\htdocs\drupal\includes\mail.inc on line 193.
* Unable to send e-mail. Please contact the site admin, if the problem persists.

pls reply asap

If problem with smtp server... pls help me configure the smtp server im using xampp which comes with mercury mail.. pls help