The speechsubmission applet does not seem to work with newer versions of the OpenJDK (see this bug report [Bug 540962] [abrt] crash detected in java-1.6.0-openjdk-1:220.127.116.11-33.b16.fc12 ).
As a workaround, you will need to install Sun's Java:
Fixed in Fedora 14 - i.e. the SpeechSubmission applet works with OpenJDK.
For Ubuntu 10.4, I used the Ubuntu Software Centre to remove:
and then install:
and the Voxforge speech submission applet worked OK thereafer.