How do these snapshot isolation level configurations interact on a SQL Server 2005 instance?
As @AlexKuznetsov noted, SNAPSHOT and READ_COMMITTED_SNAPSHOT are two different isolation levels. As such, snapshot_isolation_state indicates the former, while is_read_committed_snapshot_on the latter. Here are a few comments that I found that summarize the differences between the two:

READ COMMITTED SNAPSHOT does optimistic reads and pessimistic writes.
In contrast, SNAPSHOT does optimistic reads and optimistic writes.
~Bill Paetzke here

and ...

[READ_COMMITTED_SNAPSHOT] differs from the SNAPSHOT isolation level in
that instead of providing a reader with the last committed version of
the row that was available when the transaction started
(SNAPSHOT ISOLATION), a reader gets the last committed version of the
row that was available when the statement started
(READ_COMMITTED_SNAPSHOT).
~Uri Dimant (emphasis mine), here