I'm finally brave enough to download and begin to learn Calibre. I think it will be great.

Thank you, Koval!
But, I am having trouble finding my downloaded ebook files so that I can add them to Calibre.
I have @ 700 items in MobiPocket Reader on the cpu (running Windows XP), about 150 on Kindle4PC (some are duplicates of the MP Reader), and miscellaneous eReader books 'somewhere'.
Is there a way to transfer directly from MobiPocket Reader?
And from Kindle4PC?
If not, does anyone have suggestions for finding the 'buried' ebook files in my cpu?
Some/many of the Mobipocket ebooks can be downloaded again from Fictionwise and from Baen.
I do not know how to download the Kindle ebooks from Amazon to Calibre.
I suspect that many of you are

, but I will be truly grateful for any help.

Barb