I wonder about this Steam business...

If I download the game from them, it's an one and only download for one price?

I mean, with the disc (DVD or whatever) I can play on two computers - or on every computer I insert the disk into. How about this downloadable copy? What if my hard disk crashes, will I be able to get another copy from Steam?

My dilemma is should I get the copy on March 4th or should I wait for the hard-copy to get in shops in Romania (which might take one month, I guess)...