No need for an antivirus that much unless you're a retarded and download utter nonsense like "OMG! Download this and get free $5!", or searching on Google for lame cracks/serials and downloading them like a maniac.
On public torrent? Read each and every page of comments of the torrent you downloaded.
On private torrent? Well, most likely you'll be safe since they check the uploads, but nevertheless, read the comments and check there aren't anyone that got screwed.
Still new to the interwebs and don't trust yourself that much? Use WOT.http://www.mywot.com/en/download
You don't have to register or anything, and it doesn't annoy, it just puts a little green/yellow/red icon (based on good/suspicious/bad scale) next to any link in the page. It really helped my 7 year old brother that always keeps searching for cheats and stuff and by the end of the day his PC is full of crap.
Also, I'd recommend AVAST as soon as you install windows. Then start working on your stuff.It only needs some a bit of common sense, and logic when downloading.