Wndows vs Mac: a lost battle?

I’m managing a small windows based network (20 PC and 2 servers) in a mixed environment. The recent outbreaks of viruses/worms have prompted our dpeartmental director to lean heavily towards the Mac network, though my Windows-network wasn’t affected by any of the viruses and worms. He has in fact just turned down my request for new hardware and increased the budget for Mac. I’m wondering if anyone is also facing such a situation and how they are handling it.