I did a similar thing a few months ago, and it turned out this simple format was enough for Hudson to accept it as a test protocol:
<testsuite tests="3">
<testcase classname="foo1" name="ASuccessfulTest"/>
<testcase classname="foo2" name="AnotherSuccessfulTest"/>
<testcase classname="foo3" name="AFailingTest">
<failure type="NotEnoughFoo"> details about failure </failure>
</testcase>
</testsuite>
This question has answers with more details: Spec. for JUnit XML Output