You can specify the path to the “Site directory” and choose “Enforce listing new sites in Site Directory”, as described, when you will create a new site on the portal it will be automatically be listed in the site directory.

Configuration at Central Admin level

To configure it go to the “Central Administration” -> “Operations” -> “Site directory Settings”.You will have the same configuration as in the portal level.

In the “Central Administration” -> “Operations” -> “Site directory links scan”.

Here you will be able to define vhich view you want to scan, and if the site list have to be automatically updated.

Configuration of the scan using STSADM

Referring to the MOSS help, some STSADM commands about the scheduling of the scan:

To view the scheduling of the scan job:

   1: stsadm –o getsitedirectoryscanschedule

 

To schedule the scan:

   1: stsadm -o setsitedirectoryscanschedule -schedule <recurrence string>

 

The recurrence string indicates the frequency or the date and time at which to run the job. Examples include:

“every 5 minutes between 0 and 59″

“hourly between 0 and 59″

“daily at 15:00:00″

“weekly between Fri 22:00:00 and Sun 06:00:00″

“monthly at 15 15:00:00″

“yearly at Jan 1 15:00:00″