You can do it by hostgroup. You add the hosts to the hostgroups.cfg file then add an entry to services.cfg that is for the entire hostgroup. An example from ours:
------------------ Local LINUX GLOBAL Services definition ------------------
service_description # PING
contact_groups ux-admins, noc-op
This will do a ping (actually check_tcp which isn't exactly the same as ping but has a similar purpose - to let you know the IP is reachable). It does it on all the hosts in the hostgroup 05-local-linux-servers which is defined in the hostgroups.cfg file. Note all the hosts there have to have been configured in hosts.cfg.
I'd recommend you separate out the types of servers (Linux, Windows, HP-UX, Solaris etc...) into separate hostgroups. This way as you add services later you can make sure they are accessible from the specific type you are doing. Some commands will work on all OSs but some are OS specific.