I assume you have no knowledge of HTML, so I suggest using a WYSIWYG ("What You See Is What You Get") editor. I strongly advise Dreamweaver, but Frontpage/Expressions from Microsoft should also do the trick if need be. You can google "free web templates" and download them, open them in the WYSIWYG editor and then edit the files there directly.
if you happen to DO know html/css/etc, you can just use notepad. i suggest notepad++ if you'll be doing code editing.