How to Add a Site Template by using stsadm in MOSS 2007

stsadm -o addtemplate -filename “D:\SiteTemplate.stp” -title “Project site template” -description “Project site template with a simple structure”

After adding the site template, the IIS must be reset. The template will be found in Custom site template collection.

Ref: http://blog.gavin-adams.com/2007/07/03/creating-site-collection-templates/