In Qole's easy-debian and easy-debian-turbo-charged threads you can find two more strategies.
One is a way to enlarge the debian image.

One, recommended by Qole, is to partition one of your mmc cards, make one partition linux ext2 and to copy the debian image there.
In a post by D'ohboy there are instructions for this copy procedure.
I could not follow them exactly because some file was in another position on my N810, but it wasn't to difficult although I am completely new to Linux.

In Penguinbait's thread Console Tools you will find tools (PB) to help you partition and format an mmc card.

Google the net with "xxx linux" to find help for command xxx.

If you get stuck I'll dig out how I did it.