You just need to expand PR-T1_preloads-common.zip and the PR-T1_preloads-XX.zip corresponding to your language at the root of your READER device.
PR-T1_preloads-common.zip contains unlocalized content (music, jpeg, touch-screen drawings).
Others contains only ebooks for the corresponding language (US-UK have more books), including the PRS-T1 manual.