The movie Zeitgeist greatly overstates the case for mythological similarities between Jesus in the Bible and those predecessors. Conspiracy Science has a detailed takedown of the Horus material. Here's the most important part:

Horus was not born on December 25th, he was born on the 5th day of the "Epagomenal Days"3, which does not even take place in December on the modern or ancient calendars, but rather between August 24th and 28th, but in terms of the rising of Sirius (August 4), they are July 30th through August 3rd[4]. His mother was also not a virgin. Horus's father was Osiris, who was killed by his brother Seth. Isis used a spell to bring him back to life for a short time so they could have sex, in which they conceived Horus[5]. I, as well as several others, as well as several Egyptologists you can find on the Internet, know of no reference anywhere to a "star in the east" or "three kings" and "new-born savior"; it is simply made up. I cannot find any source or information proving he was a "teacher when he was 12 years old", that he was "baptized at age 30", that he "walked on water" (but on the Internet, I did find several places that suggest he was "thrown in the water", but I have no direct source at this time for that). More so, I cannot find any evidence he was referred to as "The Truth", "The Light", Lamb of God", "the Good Shepherd", etc. Also lacking is any evidence that he was betrayed by Typhon. In fact, Horus never died, at any time, he later merges with the sun god, Ra -- but never dies and certainly never is crucified, and therefore could not have been buried for 3 days and resurrected. If you want to look it up yourself, you can find documentation of Horus and Isis and Osiris here [6] and here [7].

As you can see Peter Joseph has a tendency to make long lists that conform to his theory, but few of the items on the list are true or real evidence of anything.

Conspiracy Science has a full accounting of the Zeitgeist movie and related subjects. It's well worth checking out, even if navigation of the site is a little tricky.

More generally, did the literary Jesus take on attributes from previous savior characters? Absolutely. That's a natural process. Does this mean Jesus didn't exist as a historical person? I'd say no. Around the same time similar supernatural acts were attributed to many Roman emperors and even the mathematician Pythagoras, and we don't use that as evidence that they were fictional.

When it comes to that long list of saviors, it helps to remember that much of what we know about other religions has been distorted by the lens of Christianity. Even if it's not on purpose, we tend to highlight those attributes of other religions that resemble our preconceived notions, and downplay those that are different. Most of those on the list don't resemble Jesus's story nearly so closely as Joseph would have you think, especially the ones from non-European cultures.