I use a contraption called a 'gripmaster' (ooh-er) which has a button for each finger. There are different models depending on your strength level...

I'm not sure how wise it is to stretch your fingers apart, but hey.... it's your hand :). As the previous poster says, it is something that comes with time. My advice would be to take your time, and try to practice every day even if it's only a few minutes - you'll be surprisd how fast it progresses.