You basically want to arrange it with the headword characters in the first column, Pinyin in the second and definition in the third, then save it out as a tabbed text file. Or, arrange it that way, select / copy out the entire spreadsheet, paste it into a Unicode-friendly plain text editor like Notepad on Windows or TextWrangler on Mac, and save it out from there as a UTF-8 text file. (this actually results in a cleaner file since you don't have Excel randomly adding quotation marks and such)