If more people got Macs, or Ubuntu, or something else, the virus/malware writers would then find it worth their time to target those platforms. No operating system is immune. They're only going after Windows because that's where they see the largest return for their efforts.

Unfortunately, the biggest problem I'm seeing on computers at work lately are root kits. Root kits come to us from the Unix world. There's no easy way to get rid of them. In the past week I've had to clean several in which there were multiple files 'watchdogging' each other, all hidden from the operating system, and they were renamed at each boot-up. Virus-checkers could see the infection but could do nothing about it. To clean them, I had to boot from a CD, then edit the registries and delete files manually. No fun.

Before you do anything hard, check your Add/Remove Programs and remove any toolbars you find. That alone may fix your problem.