Darran has released the first beta version of the JBoss Negotiation project that enables applications to use SPNEGO. Things like Windows Desktop SSO against Active Directory or SSO against a Kerberos server etc should work for you.
Please find more information here:
JBoss Negotiation Wiki
NOTE: JBoss Negotiation will be the OFFICIAL kerberos related implementation for JBoss. If not, what is the point of starting the project and working on it. You agree?
UPDATE (Nov 14, 2008): Some minor tasks plus doc work remain to go before GA. You can use the CR versions.