hm, thats a shame. i have that lib installed on my n900 already so i didnt think there would be a problem. my apologies!

my n900 shows that package is in the 'extras' repository. you'll have to install libxinerama1 it before hand-jamming the kanjipad package.
presuming you have the 'extras' repo installed (not sure if thats a default repo, cant remember back that far):
then kanjipad will either install or complain about another missing dep. if the latter, apt-get install <missing app>
^__^

EDIT:
forgot about the rootfs impact... unknown. the size of the package in the repo is about 1MB so it cant be too bad. that said, i have 36MB/15% free space remaining on my root partition. all these unoptified things add up if you dont pay close enough attention...