auto fill the missing numbers

i have recently converted an ms access program using the standard jet
backend over to postgres using an ODBC driver, i have managed to sort most
bugs out except this one

ms access already had some 57000 transaction loaded into the old database,
when i linked to postgres using the ODBC driver, all these transaction came
over, as excepted, but when i create a new record now, the database is
filling in all the missing numbers prior to 57000, which jumbles up my
record table. How can i get the postgres database to start off from 57001

any help would be a help

Regards
Greg Nissen
Systems & HR Manager
gnissen(at)geicp(dot)com
Glass Expansion
Ph 03-9320-1120