I wipe my drives all the time (once every few months), operating systems tend to get bogged down after time. I just make a backup of my files, reinstall the OS and put my files back.
When it comes to PCs not being robust, it's not the machine itself, it's the operating system. PC OSs are much more complicated then the OS that nintendo systems use. This is because the operating system on nintendo is designed to do one thing, and to do it well: play games.
There are however operating systems for computers that are specifically designed to do certain things, and there are OSs you can boot from a CD. Windows is designed to do everything, for everyone, however there are countless versions of linux out there, designed to be specifically what you want.
You don't need to buy a specific computer for certain task, just download a specific operating system.
If you want, download Knoppix:
http://www.knopper.net/knoppix/index-en.html. It's a version of linux called a "Live CD", which means it can be burned to a CD and booted without being installed on a hard drive.
If you like it, consider installing a distribution of linux that fits what you need on your hard drive. Linux is basically immune to viruses, it's free, and it can run most windows programs. Granted linux is a bit harder to use then windows, until you get used to it. I've been using linux for years now, I have a version that's perfectly designed for what I need, and I've never touched windows since.
If you're interested, here's what my desktop looks like (I'm running fedora linux):