For word,spreadsheet, presentation OpenOffice can be another option. IT Is FREE. I use it for my Windows OS. It also supports Mac Os. You can directly download it from Apple website. Openoffice is exactly like microsoft Office. Please read the system/memeory requirement before installing it.

URL:http://www.apple.com/downloads/macosx/unix_open_source/openofficeorg.html

If you already saved everything into an external harddisk, you can just load all the music into the iTunes. I think when you first install iTunes, it asks question if you want to bring your music from a location. There you can specify your external disk information

URL for iTunes:http://www.apple.com/itunes/

Hope it helps.

Cheers