Hi, I hope I can help. All you need to do is save the file as btup. No extension is required. Same for btdown. You don't have to use these names although they are easy to remember. It is much easier if you ssh into your device and use your pc keyboard. You will have a lot less mistakes. Trust me on this one. Just use vim or vi or maemopad or whatever text file editor of your choosing. At the command prompt you can do:
#vim btup
Hit enter and then hit 'i' to insert. Then type in the file info. Once you are done, hit 'Esc' ':wq' to save the file. Now repeat for vim btdown.

Post back if/when you get stuck.

I just got the N800 so I am going to try out the same thing. I haven't checked to see if this works on the N800. I need to get ssh installed but the maemo site is currently down.