You need the following files to play OpenTomb:
* Data folders from each game. Get them from your retail game CDs or
  Steam/GOG bundles.
* CD audio tracks. OpenTomb only supports OGG audiotracks for a
  moment, so you should convert original soundtracks by yourself, or
  just download whole TR1-5 music package here:
  http://trep.trlevel.de/opentomb/files/tr_soundtracks_for_opentomb.zip

  PLEASE NOTE: script file bundled in this archive is outdated, so
  don't overwrite existing soundtrack.lua file with one provided in
  archive.
* Loading screens for TR1-3 and TR5. For TR3, get them from pix
  directory of your installed official game.  For other versions
  download them from http://trep.trlevel.de/temp/loading_screens.zip