I've just published to kindle; It was a lot less painful than I expected, just time consuming.
First, there is an excellent forum you can get to from the dtp site, and I suggest you cross post questions there, as you'll have a much bigger pool of kindle knowledge. There's also some great templates people have put on their own sites.
Second, whatever format your manuscript (MSS) is in, you simply need to open it and then save it as an .html file. It's been a while since I used Open Office, but as I recall, that part's similar to MSWord, and you just choose .html from the saving options.
Once you've saved it, then run through the .html version to fix any formatting that's been changed/lost with the switch. There's nothing particularly fancy or challenging about an .html file, unless you're trying to do something clever. Just think of it as a slightly different document format.
Do you have a cover image that you want to be part of the book? And/or a map? Simply insert these, resize and center them. The site tells you what size they need to be.
For the text itself you need to insert a contents page with all your chapters listed (no details, just Chapter 1, Chapter 2 and so on. You then need to ad a book mark so that clicking on each will take you to the start of each chapter. In Word you simply use insert/bookmark; inevitably OO will have something similar, but I'll have to abandon you to their help section, unless anyone here is familiar with this and can advise.
Ideally (in my opinion) each chapter should begin on a new page; you can space the chapter title so that it looks OK on a kindle. Strangely, not everyone does this. I did a lot of repeated uploading of the file as I looked at it on the dtp site to see how it would appear. I formatted it for the smaller kindle, since that's the only reviewing option offered.
You will need to do a proofread in the kindle viewer on the dtp site. This is very time consuming (well, it is when your novel is well over 100 000 words).
The other thing you'll need is a blurb - a nice hooky description of your book to entice readers to buy it. This is not as easy as it looks, and I'm still not entirely happy with mine.
All in all, I think the concept of MS preparation is much more complicated than the actual reality. Then again, I've only just been able to download my book for real to my own kindle, so will now have to see how all that proofreading paid off!
Please feel free to pm me; happy to help out any way I can. I'm not sure how adept you are with this but hope I didn't come across as treating you like a dweeb....
Oh, and do I get a free plug? I guess mods will remove it if not...
Stormwatcher