Lets see if I can answer your questions so you may help me better.
I have an Axim 400.
The memory settings now show:
MAIN
Storage Program
Allocated: 53.65 MB Allocated: 9.89 MB
In Use: 50.34 MB In Use: 3.57
Free: 3.31 Free: 6.32
STORAGE CARD (Built In)
In Use: 0.00 MB Free: 21.24 MB
STORAGE CARD (CF Card)
In Use: 15.23 MB Free: 0.00 MB
EDITED: (It's a 16 MB CF card)
Re: Pocket DIVX - I did have videos loaded, but I've already deleted them. Don't see a place to clear the cache.
I do have some reader documents (PDF) installed on the CF card, but none on the device itself.
Yes, I do surf a lot (now that I have a wi-fi card)

I've just deleted the temp files. I thought that using the "delete temporary files" button in the explorer options would have done this for me??