I know this post is too old , but I found it by accident , and I loved to say that the problem can be solving now , any one want to view images with larg resultation and zoom in and out ,, just use the default viewer on Debian Lxde, I could view images with 10000 pxls and could zoom in and out with no problems , only little slowness with huge images ,
If u don't have Debian in your N900, then u should install it because u will gain many many useful and powerfull things that will make N900 rocks all other tablets .