I think was referring to was that by means of a site
collection, means that the contents (subwebs etc) can not live outside in a
seperate database. In other words, a site collection lives in 1 and only 1
content database.
This doesn't mean that you can't have multiple site collections in a single
database as Todd B notes. It simply means that you can't have multiple webs in
a site collection split across content databases. Nor does it mean that you can
only have one site collection per database.
For example:
http://server/sites/site1 and http://server/sites/site2 and
http://server/sites/site3
Site1 could live in Content Database 1, and site2 and site 3 could live in
Content database 2.
In Moss, you can tell it wether new sites created are new site collections, or
subwebs of the existing portals site collection
(I can't remember the MOSS admin link off the top of my head though)
But, if you want new sites to go into a new content database, you'll need to
visit the Manage Content databases list for the web application and set the "Max
Sites" value equal to the current number. Then MOSS/WSSv3 will only choose any
content databases that have "Capacity" for new site collections to be chosen.
If you create a new web application for just housing a new content database for
a new site collection, then that site collection is not related to your MOSS
portal. You could however add a link to that site in a seperate web application
to the "Sites" directory, but it's still a seperate site outside of your portals
URL namespace.