You can download other people's ships here:
http://starmadedock.net/content/
You need to copy the blueprints into your blueprints folder, and if you download a .sment file I think you'll need to use the catalog manager in the menu at the top of the second launcher screen to import it.
Find the blueprint ingame by going to inventory, then the catalog tab. Use /give_credits zebbieman 999999 to give yourself enough money to buy the ship (in singleplayer).
Try some medium sized ships before you download a 10-20 million block monstrosity, get an idea of what your PC can handle, if you download one that is too big and making it unplayable, /destroy_entity will help you.