How can I get a world's seed in Minecraft Beta 1.7.3?
use re-create button, then go to more options there you would see the seed of map you are playing. I am 100% sure that the button would be in 1.7.3, because I used to recreate maps in 1.7.2
You can upload the level.dat file to MineAtlas.com.
It allows you to see the seed. 