I have been putting Dreamweaver 8 through a lot this weekend. I found a neat section in the Preferences to add a 3rd party application to compare two files. The product Macromedia recommends costs money and I already prefer a different file comparison application called WinMerge. Well I set the preferences to use the WinMerge.exe and to my amasement it worked!
If you want to compare a local copy of a file with the file on the server you may want to change the setting in WinMerge to ignore the end of line characters for comparison. This is only required if you publish your files to a Mac or Unix/Linux web server.