two processors or more memory?

When choosing hardware for a box that will run Postgres, what is
better, more memory, or two processors?

I read that Postgres, and other databases love large amounts of
memory. I am plannning on using Postgres for several web sites that I
will host. I will use one box for Apache, and a separate box for
Postgres, which will be the only application running on it (Linux). I
am trying to figure out what would be better. Currently, there are
motherboards that support dual AMD processors, and 3 Gig of DDR
memory, or motherboards that support a single AMD processor, with 4
Gig of DDR memory. Which would be better for this application? Intel
is out of the question.

Thanks.