There are 2 iso images for the DVD install for SL 5.2 x86_64 . In most cases you only need SL-52-100608-x86_64-DVD.iso The iso image SL-52-100608-x86_64-DVD-extrarpms-security-contrib-srpms.iso has the contrib, srpms on it along with rpms that did not fit on the first DVD. The full distribtion does not fit on a single DVD.