I don't know if gqview is in the pdaxrom feeds but it's the best image viewer I've found for X11. it has high quality scaling, allows you to fit to width (hit the 'w' key), fit to height (the 'h' key), it quickly redraws the image when you're paging through in full screen and has good default key bindings for the Zaurus. AFAIK it can't read compressed files (.cbz, .cbr, .zip, .rar, etc) but most (all?) of those files are just a zip or a rar containing numbered jpg's or png's. Once you unpack them and put them on the zaurus, gqview is perfectly happy to pages through them.
-John