Ed,
I guess the answer is both, but not because there are *two* objects, but
because often these terms are used interchangeable. See SQL Server 2000 BOL
(Books online) title "Full-Text Indexes" for more details on the differences
between "Full-text indexes" and "Regular SQL indexes" as well as BOL title
"Full-Text Catalogs and Indexes".

Specifically, you *populate* a FT Catalog via sp_fulltext_catalog
(start_full) as you can have more than one table per FT Catalog.  However,
you set "Change Tracking" and "Update Index in Background" at the
table-level via sp_fulltext_table (start_change_tracking).

Hope this helps!
John

A catalog may index one or more tables. If you are only indexing one table,
it makes no difference when you run a full population on the catalog or on
the index.

If you are indexing multiple tables, you should run a full popluation on a
table basis for performance reasons. In other words, it will be faster and
you will get better performance when run populations on a per table basis.

In general you should place index each table its own catalog as MSSearch
(the engine which does the indexing) allocates threads on a per catalog
basis. So the more catalogs you have the more threads there will be
servicing your indexing and querying processes. However, there will be
greater overheard with the larger number of threads and catalogs.

Even so if you are indexing large tables you can get performance increases
by splitting the table up into pieces/child table (this process is called
partitioning) and having a seperate catalog for each child table.