You will no doubt get plenty of Windows offers, but if all you want to do is "run of the mill stuff", one of the Linux distros would be ideal.
Why use Linux?
1. Virus free
2. Malware free
3. It's free
4. Doesn't clog up and slow down
5. Fantastically stable
I could go on, but I would suggest you try one of the Live CD's on your computer and see for yourself.
How longs a piece of string? Seriously though, Ubuntu is by far the most well known and common distro. It enjoys good community support and the latest version is pretty much multimedia ready. The downside (if you can call it that), it uses Gnome as the default desktop, which is sort of MAC like in appearance. If you would like a more Windows look, so the transition feels less dramatic, try Kubuntu or PCLinuxOS.
I use Debian, but you could do with a little time with Linux before trying that. Other distros worthy of note: Linux Mint, SuSE and Mandriva, all of which are suitable for users new to Linux.
Why not download a Live CD of one of the distros and try it. Just to clarify, a live CD, will run the operating system direct from the CD and provided you set your PC to boot from the CD drive as the first boot device, you can try it out without installing.
click here for something I wrote a while back, that may help. There's all sorts of other good information on the site for beginners which you may find useful.