After installing a package, using 'ipkg -d sd install packagename.ipk'
you need to run 'ipkg-link add packagename'
so if you installed lets say opie-wordgame_1.2.0-r0_arm.ipk you would do the following.
ipkg -d sd install opie-wordgame_1.2.0-r0_arm.ipk (push enter)
ipkg-link add opie-wordgame (you dont need to add the version etc.)
and this will install opie-wordgame to your sd card.