I have an external USB hard disk that I use to store all my documents on. I move it between my laptop and my desktop PC so that when I’m out with my laptop I still have access to all my files. And when I get back I don’t have any synchronisation issues.
However, I don’t seem to be able to tell Windows Live Writer where to save my drafts (e.g. A blog folder on my external HDD) so it all ends up in My Documents.
I don’t suppose it will be too difficult to take a USB stick and copy the posts from one to the other, but I’d rather just plug the HDD in and go.
The Blog of Colin Mackay 
You should be able to use your blog hosting as your draft folder? I know with blogger I can select “Post draft to blog” which then stores it in blogger as a draft.However, I’m not sure of a way to set a default save location.
(Even though I am telling you about this, it is not officially recommended/supported by Microsoft, was not written by anyone connected with Microsoft, and has not been tested by anyone within Microsoft!)You may find this helpful:http://www.techlifeweb.com/2007/09/08/windows-live-writer-portable-20-now-with-u3/
Two excellent responses.@ben I’m going to test this out in a moment. It it works I’ll use that as my solution.@joe It does seem a bit of a convoluted route, but if Ben’s idea doesn’t work out I’ll give it a try and see what it does. However, what I’d really like is to be able to specify a blogging folder somewhere.
@ben Unfortunately it didn’t work out. WLW wasn’t able to get the draft version back out of SubText, it just picked up on the published stuff.