Need better WebSphere Application Server Performance for an application thereunder

Gang,
 
How can I increase the performance of WAS so an application running
thereunder will perform as good or better than its Windoz counterpart?  
 
 
We have installed WAS and the package application that we'd like to run
under both on a Wintel blade that runs under one of our partitions  and
we also installed it in the IFS of one of our i5 partitions; this to see
which would perform better.  We also installed a version of the package
application under regular Windoz without any WebSphere.   Well, the
WebSphere versions of the application, regardless of where installed,
runs like a herd of turtles in a cloud of wet cement, I assume because
of all that Java, whereas the Windoz version simply flys; because,
basically, its a Client-Server type of application.   I'd really like to
get one of the WebSphere versions of the application running at an
acceptable performance level.   
 
Anyone experienced something like this before and if so, how do you
make performance acceptable.
 
Thanks in advance,
 
Dave Odom
Arizona