Here are some links which may help you.
http://java.sun.com/products/java-media/speech/ (There is a list of implementations of the Java voice stuff on the Sun website.)
http://www.cloudgarden.com (30 day free trial and only $16 for a personal license or $420(I think) for developer license for 1 developer and up to 1000 distributions.) They have some example code which can help you.
I couldn't manage to download the IBM ViaVoice free trial. (A License there is over $4000 and you have to wait 4-6 weeks just to get one).
I am experimenting with the cloud garden implementation now. Using the Microsoft SAPI5 voice engine which you can get (for free) at
http://www.microsoft.com/speech/download/sdk51/. You need to train it to understand words, which can be a little annoying.
The accuracy with this hasn't been so good, but I am using the low-end microphone that came with my Dell.
The coding is a little complicated, but cloud garden's example code together with the java API should get you started fairly quickly.
Daniel