Well, there are sevaral ways to do this, but here is what I would do:
Word of caution: this backup does not take backup of the Config DB and when you are moving portals between servers make sure the source and the target servers are on same Service Pack level (WSS, SPS and SQL) - else the restoration would fail.
In fact backing up Config DB has no value. Here is what resource kit has to say:
"The configuration database is not included in the backup because it would be impossible to guarantee a successful restore of it. The configuration database that is to be restored would need to match the existing topology exactly. Furthermore, existing team sites stored across all the content databases would have to match exactly the sites in the configuration database being restored. Because there is no way to guarantee this, it is useless to back up the configuration database. The correct restore procedure indicates that you must rebuild your farm—which will rebuild the configuration database and ensures a new configuration database is created that is guaranteed to work."
You could use the SMIGRATE utility to move WSS sites from one server to another but the cavaet is that it does not move security settings.
You could also use stsadm.exe to backup a web site on the source server and restore it on the target server. Just make sure that on the target server there is no template associate to the site on which you are restoring the backup.
The other way that i find very useful to move sites from one site collection / server to another is using FrontPage 2003. You can take a backup using the Backup Site command under Tools >> Server menu. This creates a FWP file which can be used for restoring via FrontPage on the target server / site collection.
A great resouce on backup-restore and migration can be found at: http://www.microsoft.com/technet/prodtechnol/sppt/reskit/c2861881x.mspx
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