I don't know where the idea of using apt-get update comes from. With Knoppix, you will often risk to make the system unusable running it, either because of package/library/etc incompatibilities, or because of overflow of persistent storage because all the updated material - which upon update is no longer compressed - plus package copies is stored there. So updating is best done on a package basis, when needed. In no case you can get along with just 256 MB, running any more extensive form of updating, you should really have the full 4GB available. With Knoppix 6.2.1, no updating has been necessary for me to install Flash, I have downloaded it from Adobe and used the dpkg -i command, with no problems at all.