Microsoft Office is separate from and does not come with any flavor of Windows. Wordpad can't open either the older .doc or the new .docx document formats. So yes, if you want to open and edit .doc or .docx files you'll have to buy Microsoft Office -- or at least Microsoft Word. Here are some of your options for legally paying less than full price for Microsoft Office 2010:
First, if you're a student, you may qualify for the Office Professional Academic edition of Office at a pretty good price ($79.95):
http://www.microsoft.com/student/
Second, if you’re interested in buying just Word, check out this URL, especially the second group of listings.
http://office.microsoft.com/en-us/products/FX101754511033.aspx
Note that the higher of the two prices quoted is for a full version of that program and the lower, for upgrades from existing software. Read the list of upgrade-qualifying software carefully: MS Works is often one, and may have come on your machine.
Finally, if you're willing to spend a little to save a little, Microsoft Works is available in stores for about $40.00. You could buy a copy, install it, then buy Office at the upgrade level. I think you'd come out ahead. Note that the upgrade copy probably checks your machine for Works' presence, so don't get rid of it after you've installed Office. You never know when you're going to have to reinstall Office.
Hope that helps.