Data Security on Windows Machines?

mcskoufis asks: "I am running my own company from home, offering various Internet related services to customers. I have rented a server which runs Linux and there are no current security or performance problems. However, because I cannot afford to have a business site with several geeks investigating into network security, I have some sensitive data on my Windows box at home which need to be safe from malicious marketers/kiddies having fun/etc. More and more marketing companies are working on very dirty tricks to gather email addresses and also turn windows (mainly) machines into mass mailing servers without the owners knowledge. With the latest worm attacks and also the sophistication of them, I feel even more and more vulnerable each day. Bearing in mind the fact that it is impossible to switch to Linux at home for a number of reasons and also that because of the business I need to be online 24/7/365 what the Slashdot community suggest as the best way to have a secure environment for my data while using Windows? Anti-virus software has proven to be not enough and firewalls create problems while performing daily business tasks on the server from home."