Yeah, I don't know it is the best UX for vagrant. To make things worse there is a limit to the size of files you can upload via personalization.

I have a couple different ideas. First, if you think those files are going to be standard to bootstrap windows on Rackspace, we could just include have some kind of windows flag/detection which would add those files under the cover. The second idea, would be to use the personality functionality and have a source and destination keys that would do all of the encoding for the user. (We could use :path and :contents for advanced users). We could also try to do something with vagrant init to generate something for windows. 

Do you like any of those ideas?