Making SELECT COUNT(seed) FROM fast

Hi all.

I have a table with about 5 million rows in it. I need to be able to get the
exact number of rows in the table at runtime. So I tried the following:

xxx=> explain select count(seed) from mytable;
NOTICE: QUERY PLAN:

Aggregate (cost=103152.27..103152.27 rows=1 width=4)
-> Seq Scan on mytable(cost=0.00..89756.42 rows=5358342 width=4)

EXPLAIN
xxx=>

Actually executing this query takes about 2 minutes on a P3-800MHz machine
with 512MB of RAM.

I have an index on the seed table, and I have done VACUUM ANALYZE on the
table after inserting the rows. Is there any way I can get this to be fast?

Thanks.

Gerald.