Wow, what a wonderfully friendly forum, that's a rarity these days
Thanks to all who replied, there is some useful information here. I'm realizing though that I really can't do much until i have the Reader in my hands so I can see which format works best for me. I've been reading the forum all day trying to sort things out - there is a lot to learn.
From what I've read, I might try to work with RTF format. It seems it would give me a bit more control over formatting than TXT. EPUB sounds nice, but all this talk about mystery line numbers is scaring me off. No other formats are very appealing right now.
So I guess I just sit tight until mid-March when I can actually load up some books and experiment! Who knows, maybe my TXT files will look good straight away...
Thanks again!