Thanks for the info, Hein! I do have some additional questions, though:
1. I copied (as root) tv-grab-file to the /usr/bin directory, and made sure it was set as executable. Tvheadend's web interface doesn't show tv-grab-file in its XML-TV Source drop-down, even after restarting tvheadend. I can only see the services that were listed before. What should I be looking for exactly? Have I done that right?
2. The tvheadend daemon seems to run from root. I can access it from a remote computer no matter which account I'm logged into on the media center computer, or even if logged out. Where exactly should the tv_grab_file.xmltv file go? Should I place it in the {home folder}/.xmltv/ of every account that accesses tvheadend, including remote computers, or somewhere in the root directory of the media center computer?
3. How do I automate the actual data grabbing with zap2xml? I've read that I need to set up a cron job that daily runs the zap2xml script to create up-to-date xmltv files. I don't know how to create that cron job, however.
I've been using Linux for many years, but when it comes to scripting and installing/configuring things like this by hand, I'm a complete noob! Give me a .deb file to install, and I'm fine, but something like this is a bit foreign to me. I appreciate your patience and help!