1) untar to some directory like /var/www/ (it will untar into a 'netmrg' directory)

2) modify you apache config to alias /netmrg to /var/www/netmrg/www
  Alias /netmrg "/var/www/netmrg/www"

3) setup the database
mysqladmin create netmrg
mysql netmrg < netmrg.mysql
mysql
  grant select on netmrg.* to netmrgread@localhost identified by 'netmrgread';
  grant all on netmrg.* to netmrgwrite@localhost identified by 'netmrgwrite';

4) add a user for yourself
mysql netmrg
  insert into user (user, pass, permit, view_type, view_id, fullname) values ("admin", encrypt("admin", md5("admin")), 3, 0, 19, "Administrator");