Lemme just say this. I was in class one day with my VISTA laptop. A girl in class that has a Macbook comes up to me and says "Can I use your laptop? I can't figure mine out. I should never have got a this thing". She admitted she believed the Mac hype at first but after getting one, she was sorry she did and thought all that stuff was bullshit.
My brother. Such a Mac nutswinger that he continued to use an ancient G4 iMac with his recording/mixing hardware and software and get this, IT CRASHED...... A LOT. Well when he finally has money, instead of buying new hardware, Mac or otherwise, he gets a used Mac that's still compatible with his hardware. A Dual G5 Power Mac. Guess what, still crashes on occasion and it cost him $800. Too damn much for hardware as old and week as he got (yet it was considered a steal for a Power Mac, ri-fuckin-diculous). He still has slow ass dual G5's with 1GB of DDR400 RAM and a GeForce FX5200. For essentially the same cash I have an Athlon X2 6000+, with 4GB of DDR2 800 RAM and GeForce 8800GT. He coulda got something more powerful (though not as powerful as mine) and new hardware/software compatible with Windows for just a bit more cash.
Viruses, like James said, just don't be a fuckin moron and you can get away with runnin Windows with no probs. Practice safe surfing (use something other than IE and avoid questionable sites and links). AV, just get something free like AVG or Avast if you are worried. They work just better than most paid AV's and if you aren't an idiot you won't even need them. I keep it just in case cause my parents like to borrow my PC occasionally.
And if you are still SO worried about all this shit with PC, GET LINUX. Or fuck, even get some kinda UNIX. Oh wait, OSX is based off UNIX, holy shit. You get many of the same advantages as Mac only with hardware that is way cheaper and non-proprietary, and guess what, the damn OS's are mostly FREE. Dual boot Windows and Linux/UNIX. Then you can have it all.
And if you can't tell by my tone, I think Macs suck. I hate the damn things with a passion.... well for regular use. If video or image editing, Mac can be useful but if you have the right software and know what the hell you are doing, PC CAN DO ALL THE SAME SHIT JUST AS WELL.