While getting a mac or linux "box" (macs arent really boxes) is a great way to avoid virii and other nasties, macs code is no more clean or secure than microsofts. There are simply much less people looking for the bugs, glitches, and holes in their software.
BTW how big is a OSX install? XP runs about 2 gigs and last time I played with linux (red hat and mandrake) it was a little over 2 gig. + 200 mb upgrade.
Routers are nice. Most allow you to open up specific ports very easily. I actually have a couple of programs that require me to open ports and once I actually read the help files with those programs that told me which ports to open I was set.
Mozilla programs are great. I was using their browser until I found opera and even then I was using their mail client for about a year. I recently found that they had just a mail client "thunderbird" for download and I love it. Along with IE, Outlook is commonly targeted by hackers and spyware. switching from them is easy enough as most others allow you to import bookmarks, mail, and contact lists.