Step 5 in the INSTALL file says to set four server parameters to enable statistics collection (stats_start_collector, stats_command_string, stats_block_level, and stats_row_level). It appears that as of PostgreSQL 8.3, these parameters were removed/renamed/merged respectively (http://www.postgresql.org/docs/8.3/static/release-8-3.html) and the correct parameters to set are now track_activities and track_counts.
This was fixed in commit: https://github.com/phppgadmin/phppgadmin/commit/202be379e6e7cf7ad217d945d367fff448cb7256