Are you working in Dreamweaver, and using the design view to paste the code in? If so, when you copy text from Word it comes with a bunch of default styling -- a lot of which is invalid for web design and causes display issues when it overrides your existing styling. Your best bet is to copy the text from Word, paste it into a plain text document like Notepad to remove any styling, and then copy/paste that text into Dreamweaver.
Alternatively, instead of using the "paste" command to paste content from Word, another option is to go up to Edit -> Paste Special, and select the "text only" option. I believe that will remove any Word formatting as well.