Let me start with remarking that it's very very important to have a backup of a very very important document, just in case it gets corrupted. Not everybody does realize this, but most people learn it eventually.
There shouldn't be such compatibility issues between Word 2003 and Word 2007. It's rather easy to proof, in fact, that there aren't, by repeating the experiment on a fresh uncorrupted copy.
Without a backup (a previous copy of the still correct version) I'm afraid you lost the info. Did you already try to access it across the network from Word 2007? If it's incompatible (which it probably isn't) the info might turn up again.
I had typed a somewhat long, and very very important document, which version of office I created it in, I'm not sure. At some point I noticed that at least 3/4 of the entire document was changed, changed in a very negative way. I realized that all my work had been replaced by a bunch of \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
It is possible that this happened as a result of accessing this text document on a network between two computers, the newer computer accesses the document with Microsoft Word 2007, and the older computer accesses the document with Microsoft 2003.
It would be a great blessing if you could help me fix this problem. Thank you very much