@Sulu,

Thanks for the exhaustive answer. I have a question about the multiple/replacing images.

Originally, I was unable to extract the compressed image on my N900 after downloading it from the Maemo repository (continual "out of memory" messages, no matter what I tried).

So instead I copied the comnpressd image onto my XP machine, extracted it with 7Zip, and moved extracted image onto my SD card on my N900.

All that worked out fine. But now when I go to "replace the image" as you suggest - I understand this to mean, simply copying the extracted image back onto the N900 over the current one - I discovered that it seems to be exactly the same setup. (The only thing I added was AVIDemux, and it's still in the menu, but it doesn't seem to actually run if you select it, though).

So,maybe you could explain a bit more. I am a tweaker by nature, though, even though I am woefully ignorant of the technicalities of things, so I will persevere and not be daunted by the problems. I usually find my way by stumbling through! Thanks for the help.