If you choose to run any version of Windows, you are making yourself a bigger target for malware, hackers, etc. than if you run an Apple or Linux operating system. I prefer Ubuntu Linux myself. You can learn more if you visit http://www.distrowatch.com.
The great things about Linux are that it is FREE, it includes a Microsoft Office compatible suite called OpenOffice. Also, it is possible to dual boot Linux and Windows. Linux needs only about 20 gigabytes of disk space to run. It also can be run from a "Live CD," which allows you to get familiar with Linux and not install it on your hard drive.
If you choose to use Windows, keep it updated and back up your data regularly. Also, get the Firefox browser (version 3.6.13 is best) and install the NoScript and Ghostery add-ons. Avoid using Internet Explorer but install any updates from Microsoft.
To download Firefox and other security software (both free and pay versions) go to http://www.majorgeeks.com. To scan an infected PC without bringing up Windows, use this Kaspersky application:
http://majorgeeks.com/Kaspersky_Rescue_Disk_d6501.html
Hope this information was helpful.