Norton AntiVirus for Mac is Symantec's full anti-virus package for Macs. Norton also makes a free anti-virus for Mac called
The first thing to note is that, generally, Macs don't need anti-virus software, although there has been an increased threat in recent years. In fact, until recently, Apple claimed that Macs do not need anti-virus software at all although they have quietly dropped that in light of recent outbreaks.
The second thing to highlight is that Norton AntiVirus for Mac is very heavy on your CPU, as it runs lots of background processes and it may slow down your Mac. Norton AntiVirus can also be overzealous about threats and flag things that may be dangerous on PC but probably aren't on a Mac.
Most recently, Norton AntVirus for Mac has been updated to work on both Lion and Mountain Lion but it's still a hefty package. Version 11 of Norton AntiVirus still works on OS X 10.4-10.6. The good thing is that both versions update at least once a day to stop late-breaking threats and it extends to scanning IM clients for suspicious attachments.
Be aware that removing Norton AntiVirus for Mac can also be tricky, although Symantec publishes full instructions.
Norton AntiVirus is a very heavy anti-virus solution for Macs but if you can handle the sluggishness, its worth a try.