I assume the the task takes longer than 5 seconds to complete? Are you running the same OS? Can pgsql distribute the load on both Xeon processors? Is pgsql custom compiled for a specific architecture (Pentium III, for example)? How do you measure the response time? Are there other apps involved?
t.n.a.
The DELL PIII box runs FC4 , the config is the default one. The DELL Xeon runs SUSE 10.0, the config has some changes to improve autovacuum, thats all. I just downloaded the source and follow the tipical install instructions on both machines. The application takes the start and end time of the query, mainly it is a reporting application running on a WinXP client.