I experienced the same problem with PG 7.0b3/ AOLserver3.0b61, Mandrake/RH6, but didn't know enough to fix it. Dataload problems have far-reaching consequences, so I'd recommend logging this process. Anyone with problems might like to look there first.
However, in case you can use the specific information of where the problems arise, here's the errors grepped from the log of the load-data-model.sql. Only the homepage.sql ERRORs seem to be a problem.
psql:homepage.sql:1027: ERROR: Function 'trunc(int4)' does not exist
psql:homepage.sql:1028: ERROR: Function 'power(int4, int4)' does not exist
psql:ecommerce-plsql.sql:700: ERROR: ProcedureCreate: procedure ec_items_reportable_count already exists with same arguments
psql:events.sql:19: NOTICE: plpgsql: ERROR during compile of administration_subgroup_add near line 54
psql:events.sql:19: ERROR: parse error at or near ";"
psql:sdm.sql:45: ERROR: parser: parse error at or near "("
This mainly affects the working of homepages - had these up and running under PG 6.5.3.