If you need to do any of:
Otherwise, one of the Linux distributions such as I named above will be lower cost, more robust, and much less susceptible to viruses and malware.
I run both Linux and Windows myself. I have a couple of Windows boxes for serious gaming, a Windows box for Quicken (I'm a serious user of online banking) and several Linux boxes for various purposes. Almost all my web browsing and document production, as well as my calendar and address book, are on Linux. I use Linux for image manipulation and scanning (but I'm not addicted to Photoshop - Gimp or Pixel is sufficient for my needs.)
Bottom line - we can't adequately recommend what operating system you should get until we know what you need to run on it - the applications you need.
My excellent slide/film scanner will not run on anything but Windows. I'm guessing this is unusual, but you do need to consider things like this.
Ish... I don't like any of those distros... I'd recommend Mepis 6(on july 10th) or PcLinuxOS