I've just completed my migration of old posts to this new blog. Method I used for it isn't very nice however, it look like it is successful. I basically wrote some code to export posts from DB into a private format and programaticly imported those into BlogEngine. It was bit time consuming, however, tags/categories/comments etc are well preserved and it worth the effort. I've also added 301 redirects from old URL to new ones; it was not that difficult as SEO titles of post in the old and new system are same.

Also, my first attempts at code formatting in BE were unsuccessful. I am not looking for colorful code, just enough to highlight the code and if possible, to use line numbers. I'll play with BlogEngine and see whether I can manage a simple highlighter for me.