I know most of you can't mess with saves on your retail cards yet (and by extension can't do editing that requires a pokewalker), but it sounds like you may not be waiting much longer. I shelled out for a hardware dumper however and took a stab at finding the offsets relevant to the pokewalker.
Here's a dump of the notes I've taken, offsets in hex from beginning of the current block:
e5dc - 02 when a pokemon is on the walker, 01 when not?
e5e0-e667 - pokemon sent to pokewalker (136 byte encrypted as usual)
e6d4 - course selected
e704-e707 - steps taken to date
e708-e70b - watts
e70c-e70f - courses unlocked bitfield (27 courses total)
I've noticed the addresses e5de and e700 changing as well, but haven't figured out how they're relevant.
I can't promise that this list is every address related to the pokewalker, but I've covered the major stuff. One thing I'd like to know more about is if there's any kind of unique pokewalker-ID stored in the save to tie one game to one walker. (Seems the identification information is stored on the pokewalker side; my guess it it's just the ID, SID, or both of the current player.)
Enjoy.