It's a "patching/auto-updating/download/server browser" software. Please tell me why it needs a 1.0Ghz system with 256MB of RAM. We all know all this HD space is needed since Steam download stuff while your not looking and that internet connection because your fucked if you're on 56k. But why would it need a 1.0Ghz CPU with so much RAM. Since the only thing you were able to use it for in the beta was playing a 5 years old game.
They recommend a fast fast system such as that because Steam creates a "cache" for the games and suc that you download. The caches are single-file archives which tend to become rather large. If you've ever compressed/decompressed large zip/rar/ace archives then you'll understand why they recommend something better than a 200MHz Compaq with 32MB of RAM.
In any case, you can get a processer which is faster than that, a mobo to support it, and 256MB of RAM for around ~$100-150.