Kara,
Do your 500 ebook files end with an extension of ".rb". If so, they need to be converted to ".imp".
I was in the same boat as you but (going from an RCA REB1100 to a EBW/ETI2 & ETI2). I used the GEBLibrarian though. GEBLibrarian is not free but its cheap.
With this I was able to take all my ebooks from my old RCA reader and convert them for use with both of my "new" ebook readers.
Hope this helps.
Bob
PS - Say hello to my folks in Alabaster. Tell them their son in Minnesota is freezing!