I prefer Google Docs for manuscript writing and collaboration, but if you like the features of Microsoft Word, the tutorials below may help you track changes when collaborating on a document:
Track Changes: Word 2007 Tutorial Menu. Florida Gulf Coast University.
Microsoft Track Changes - Word 2007. Paper-Check.Com.
How to track and manage changes in a Word 2002 and a Word 2003 document. Microsoft.
Google Docs & Spreadsheets Could Replace Word & Excel for the Average User
Image source: OpenClipArt, public domain.