Just to be clearer than in my previous post, which explains everything, I'll say what you should do in this post--
Learn to edit on your own. If it's grammar you're struggling on, find a good book on English grammar and mechanics. If grammar isn't the primary problem and you are also having trouble with the revision process itself, you should get more practice editing, but perhaps not your own things. Maybe put your own manuscript away for a while and head over to the Share Your Work forums and try your hand at editing some other peoples' work.
Also--for anyone else fed up with MS Word for other reasons and came to this thread with other problems in mind, I'll recommend OpenOffice.org. It's free, open-source software for Windows, Mac, Linux, etc., that replicates almost everything that Microsoft Office is supposed to do. Since it's free, there are obviously some aspects that aren't as good as MS Office, but there are also things that are even better. If nothing else, the price is right. I think it's certainly a better alternative for an upgrade than Office 2007. And if you're a Mac User, try NeoOffice. It's what I use, since the OpenOffice.org mac version uses X11, which I find very annoying. NeoOffice is based on OpenOffice.org code, but words natively on Mac OSX. Free yourself from the chains! Don't give in to MS Word.