I would suggest that you go to a bookstore such as Barnes & Noble and find a Linux magazine that contains a DVD that has an Ubuntu 12.04 that you can install.

Insert the DVD in your player's tray and start the computer. When you see the first screens come up press F12 or what it indicates to get the boot menu. With the arrow keys select the DVD player and press the Enter key.

The install screens will help you configure your region, keyboard, user name, password, etc. Choose to use the entire disk for Ubuntu. Be sure you're connected to the Internet and choose to get the updates as Ubuntu installs. Once the install is done (over 30 minutes) you will be asked to restart the computer.

I would recommend that you click on the top left in the menu list and type:
Update. You should see Update Manager in the window that appears. Click it to start it and let it get the remaining updates.

When done, you've got a modern operating system that is fast, reliable and with lots of useful software already loaded and ready to go. LibreOffice is the equivalent for Microsoft Office and it's got nicer capabilities along with being easy to use. You don't need an anti-virus product.

Happy computing!