to get the data from the form: use the CGI module.
to get the data into the DB: use the DBI module.
i don't know if you're alreay familiar with the DBI documentation, if not, you will find some examples in there.

untainting all user input is an important thing, however, if you're using DBI.pm you may want to use placeholders; there's also a section on that in the DBI docs. if you use placeholders then DBI will take care of quoting the actual data correctly; but of course it will be helpful to additionally look into the data before if it contains the format you want.

about the cronjob: why don't you want to use a DB-connection directly? only if you expect high traffic this can be a bottleneck, but then i would consider using mod_perl instead of CGI, so the db connection can be programmed persistent.