I also faffed around trying to convert PDFs to EPUB with Sigil and Calibre but couldn't do it within a reasonable time-frame. Thats despite a computer science degree :P
Basically unless your an expert don't bother trying to convert the files to epub in Calibre.
The sony reader handles PDF files pretty well and In my experiance Calibre doesn't do a good job of converting them to EPUB. Correcting them manually in Sigil is too much work.
For the best experiance purchase/download books that already come in the EPUB format. The sony readers very easy to use if you stick to the basics
