DB and PostgreSQL on dual processor Mac OS X

Hello, I have a data warehouse application I've built with PHP 4.3 and PostgreSQL 7.3.2 running on Mac OS X 10.2.6 on a dual 1.42 Ghz G4. I've noticed a performance issue with my application when using PEAR DB 1.4. If I launch a complex select query (PHP page) from 3 different browser windows, I see 3 Postgres processes in Top. The first one uses >95% of one processor and the other two use 0%. When the first one finishes, the 2nd uses >95% of one processor and then when it completes, the third process finally gets a turn. If I do the same query in 3 different windows with phpPgAdmin, all 3 Postgres processes execute immediately with each immediately getting about 65% CPU. I've tried using both persistent and non-persistent connections. Does anyone have an idea what DB is doing differently than phpPgAdmin that might explain this behavior? Thanks, Greg