It's easier to do what you want by using a desktop publishing program than with Word. (DTP is far more flexible, with much more professional looking results). If you've got Microsoft Publisher, that's what you should probably be using. Otherwise, this is free and will do what you want:
http://www.serif.com/...tware/?mc=FSSPAGEPLUS
Instructions for Word vary greatly across different editions. These are for Word 2007:
Click the Page Layout tab.
If you've not already done so, go to Orientation, to select Landscape format.
Then go to Columns >2
When you start typing, you'll see that you text only occupies the left-hand side of the page but it will automatically go to the top of the right-hand column when the first column is full.
To widen the gap, highlight all of the text on the left side and increase the 'right indent' size. Then highlight the right-hand side and increase the left-indent figure.
Be warned, though, things can get very fiddly in Word. If you use a DTP program you can simply start with a completely blank page and draw text boxes in each half. It's far easier!
Chris