Maximum number of web sites and Sub sites in MOSS (SharePoint) site collection

The total number of web sites and sub sites together in one site collection should be 2, 50,000. Web sites which are actually the first sub sites under a site collection, and sub sites are the sites under the web sites.
So if you've got fewer web sites, you can have more sub sites. But for better performance use not more than 2000 sub sites per web site.

MOSS 2007 Performance guidelines for number of sites
Click here

Guidelines for acceptable performance for number of sites
Click here