Pre-translating a large rich-text document

This one is tricky... (and not so practical just yet) So let's say you have a 120 pages document, written using MS-Word, and which is understood pretty well by Writer (v2). Now let's say your document is a technical document and, as such, it is half-full of screenshots taken from a software interface (in this case Dokeos) directly into the language of the document. See what I mean? Now, let's say this document is in French and you want to translate it to English (or Spanish, the problem is exactly the same).