I made
this soft keyboard roundup a little while back while I was looking for a solution. There are several ways to go. I chose Tengo Thumb b/c it has only 6 buttons and a large dictionary and is very easy to learn. You can use a finger or your thumbs. I also like that it didn't take up much screen real estate.
However, that's my taste. There are many alternatives and some of this software is free or has free trials. Fitaly is popular and has a new version (which isn't yet in my roundup), and there are some nice full screen apps as well. I suggest you read up and do some trials.
Good luck and have fun with it. BTW, on Aximsite, if you do a search for Stormloader, that user developed a flash based keyboard that's free and quite excellent. It's not on my roundup yet either, but it will be shortly.
Steve