Fawk spending 2-3x as much for a Mac. If you like OSX, just buy a PC and install it on there. I like Ubuntu a lot, but I wouldn't recommend it to my grandmother. People think Windows is a pain in the ass... ha.
Otherwise, use Firefox or Chrome. Keep up with Windows Updates, install an anti-virus application, and fix whatever bad browsing habits that got you infected with some malware in the first place. Rarely have I run across an infected machine where user error wasn't ultimately to blame.