thrashing like a beached shark

Hi, I've been using PostgreSQL for a few weeks, and I can't stop it from
crazy thrashing. I've got a few tiny tables, total of maybe 2k of data,
and yet a series of simple selects repeated on one small table causes
postgres to access the hard drive every single time. Shouldn't it be
buffering a 2k table? According to the docs, the default buffers should
have half a meg of space. I even tried calling postmaster with -B 128, but
that didn't help at all. It also doesn't seem to matter whether the tables
are indexed or not -- I suppose indexing isn't used when tables are that
small. Oh, I forgot to mention, there's just one persistent connection to
the database through libpq++. I'm running 6.3.2 under linux 2.0.35.

Thanks for any help!

adam