the error you get indicates that the jar file containing MQEnvironment (com.ibm.mq.jar) is not in the classpath.
you did put it in jvm/lib/ext of the Notes or domino program directory along with the other jarfiles that are already there, right? (you put //jvm/lib/ext in your first post.)
I don't recall if 8.0 designer client has typeahead for java, but assuming it has, you should get typeahead if everything is correctly configured.
Other than that, i can only say for me MQ 7.0.1 works with following jars included:
some might not be required, but i don't know.
Feedback response number WEBB8PBLFD created by Jo Willems on 12/07/2011