At least 25GB, preferably more than 30GB if you plan to run it for more than a few months. The blockchain is rather large (just under 20GB right now).
If you want to run a light version of bitcoin, try installing multibit or electrum. If you want to just mess about with bitcoin then run bitcoind in testnet mode (only requires just over 1GB of space); testnet bitcoins are free!
cool! Thank you sooo much! Is there a tutorial to show how to install multibit or electrum to CentOS through Mac SSH (terminal)?
Thank you,
J