Hibernate maps java.util.Date to java.sql.Date when serializing to DB, and returns java.sql.Date when deserializing. So you can get some class cast errors on compareTo if you are using JDK1.5.
I have copied DateType and TimestampType classes and modified them to return java.util.Date in get method.
Then I've placed them into separate jar and then I've tried to include this jar in CLASSPATH before hibernate.jar. So modified classes are loading instead original. It looks like all is ok now.
Is it good way for solving such trouble? Is it possible to change hibernate Type-clases to return java.util.Date?
I can upload modified classes if you want to see them.

Your solution is okay, but Hibernate will not be modified there - this has already been discussed extensively on this forum, just do a search.