I am trying to visit both sites before closing. Need help in getting from Panthenon to Capitoline Museum. Is it faster taking a taxi, metro or walking?
It's about a 15-20 minute walk, and an interesting one at that. Google Maps "Get Directions" is a great resource for these sorts of questions. Click on the pedestrian icon for walking directions, distances and estimates of time. Metro is not an option, as you can also see from Google Maps which displays the Metro stops, none of which are anywhere near the Pantheon. (And, btw, it's "Pantheon" - no "n" in the middle.)
It's only a half mile or so walk, so even though taxis are cheap in Rome you wouldn't save much time. So enjoy the walk.
Those two sites are not that far apart. I'd walk it, and have. But pay very very close attention to the map. There are many opportunities to take a wrong turn and go hopelessly in the wrong direction. It happened to me on that route and took twice as long to get there. And I'm a guy, so I'm not supposed to ask for directions!