if you want an OS which you can browse the web on then Ubuntu is probably the most easy to use, though like Eero said, the performance wont be great. Wordprocessing is kinda difficult cause you're stuck with either web-based ones, or open office, which sucks the left one.
If you wanted to actually learn some linux, I suggest checking out Arch linux. It gives you a bare-bones installation, without a GUI or anything, and you have to learn how to install each of the bits. I've been using it as my desktop OS for the last 4 years now, and it's worked perfectly as a browser, mediaplayer (VLC), programming interface (various languages), and chat (pidgin) which is all that I really use. You could also learn to produce professional grade documents/papers/etc with (La)TeX, and the editors on linux are good enough.