With no offense intended to anyone, my advice would be to stay away from all things Norton. I had Norton Anti Virus on my PC for a long time, and I could not believe how incredibly intrusive it was. It almost literally welded itself to my hard drive. It was everywhere. I received what seemed like continuous pop ups warning me of one thing or another. It was amazingly frustrating to have on the machine. I eventually uninstalled it (and Norton Personal Firewall too) and now have a much more peaceful PC experience... when I have to use my PC.
The upshot of this is that I would strongly advise against installing anything Norton on your Mac. Why mess with a good thing?
Some folks who also use PCs may be wondering if I have not left my machine wide open to attack now. I have not. I use Adaware, Spybot and ClamAV on the PC, on a regular but manually controlled process, to be sure the machine stays clean and healthy. The key here is that these things only run when I tell them to, not continuously and intrusively.
For a firewall, I depend completely on my FiOS router for this function. The same can be done for those with DSL routers. If you doubt the effectiveness of this, turn off all of your firewall software, and point your browser at:
www.grc.com
Scroll down an select the Shields Up! functionality, which will probe your machine from the web side and report what it finds. This is equally useful and informative for you Mac as well by the way. With just my router's firewall in place, my PC is invisible. That is proof enough for me that I don't need anything else. Use of "smart computing" rules (don't click on attachments in suspicious emails and things like that) and the occasional scan with Adaware/Spybot/ClamAV keeps my PC happily (and inobtrusively) clean and healthy.