select count(*) from anIntColumn where int_value = 0; is very slow

Hi

we have a table with about 4 million rows. One column has an int value,
there is a btree index on it. We tried to execute the following
statement and it is very slow on a dual G5 2GHZ with 4 GB of RAM.

explain analyze select count(*) from job_property where int_value = 0;

Aggregate (cost=144348.80..144348.80 rows=1 width=0) (actual
time=13536.852..13536.852 rows=1 loops=1)
-> Seq Scan on job_property (cost=0.00..144255.15 rows=37459
width=0) (actual time=19.422..13511.653 rows=42115 loops=1)
Filter: (int_value = 0)
Total runtime: 13560.862 ms

Is this more or less normal or can we optimize this a little bit?
FrontBase (which we compare currently) takes 2 seconds first time and
about 0.2 seconds on second+ queries.

regards David