java -version returns 1.5.0_01, thought so. Bit of a bummer on the JPG thing, but OK, that's fair enough. And yeah, Irfanview's converter option was what I used to get those files working - I've now got the full Azumanga Daioh set ready for the trip~ Thanks for this tool - unlike manga2book, JE-Comics actually puts the pages in the right order!
