To create your custom distro, click on the Designer link on the Instalinux homepage and select your base distro. You currently have a choice of CentOS 4 or 5, Debian Etch, Fedora up to version 8, OpenSUSE up to 10.3, Scientific Linux up to 5.0, SUSE 9.3 or Ubuntu up to Hardy Heron.
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For the new distro creator, it certainly beats having to download all the source code over a domestic broadband connection, then figure out how to build it. The setup is very straightforward, and it supports a range of base distros. The only questions you have to answer in SystemDesigner are the same ones you would have to in a standard install.