What blogging software are you trying to do this with? Some blog applications already have add-ons that allow you to export posts, although I've never heard of any that will do everything you're looking to do.
Here's a few ideas if you were to develop your own solution:
1. (This approach would need access to the blog's database.) You could create a query that collected the posts you wanted, and then export those records as something you could convert. It would probably be very tricky to automate the conversion phase of the process since you would also need to create format tags. I'm thinking the best bet would be to go with an intermediate XHTML file that could then be processed into the desired offline format.
2. There might be a way to leverage RSS to generate the file you need for subsequent conversion.
FWIW: I'm guessing you're going to need to develop your own solution. When it comes to blogs, popularity is the name of the game. Since most bloggers are trying to attract site hits (and
click revenue), I don't think there's a huge demand out there for software that basically allows somebody to read content without visiting the blog itself. Most bloggers would consider doing something like that tantamount to 'scraping' their own content.
Luck!
