You should try with decode(..., ..., ...)
select
decode(seqnum,
1 , '1',
cnt, '0'
) as value1,
decode(seqnum,
1 , t.BEGIN_DT,
cnt, t.END_DT
) as TIME1
...
here's the link to the documentation of decode.
However, as has been pointed out in a comment, the join
construct (ansi joins) won't work in 8i either.