The database is very slow !

I currently have PostgreSQL 7.1 installed on a server with about 700
Mb of RAM.

I have many problems of speed with a database I created. For example,
it took almost 12 sec to run the query "select * from table" directly
from PostgreSQL, on a table with 4000 records and 60 fields ...
And the whole application built on this database is very very slow
(some pages take almost 20 seconds to load !)

I verifed the indexes, I think they are ok, and I tried to make my
queries as short as possible (without select * but with select
field1, field2, ...)

But anyway, I guess there is a problem of speed directly with the
database, because I think that is not normal to need 12 sec to run a
query on a table with only 4000 records ...

Has anybody an idea ?
Thanks
Krystoffff