A service is something that is started when the operating system loads. even before someone logs in, a service will be running, even when someone locks the system, or logs out, the service will remain running. you can stop it if you need to of course, in the administrator/services control panel applet.
Installing the client (RC-5) allows it to run hidden from users, since there is no icon in the system tray. It also allows it to run reguardless of who is logged into the PC, so you dont have to install it for every account.
To install the RC-5 client as a service, install the client normally, configure it, and then make a shortcut to the dnet.exe with the command "-install" added after the path, double click the shortcut, and bang! "The client has been installed as a service" or something similar to that will show.
As for SETI or other distributed programs, Im not sure how, but I think its possible to install them as serices also. Check the link above, it looks like it has some nice resources. Enjoy!
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