Re: difference b/w portalRenderQueue and
portalPreRenderQueue

first off these queues/pools are only used if the portlet's forkRender and
forkPreRender properties are set.

renderQueue is the thread pool used to render portlets during their  render
phase. preRender queue is the thread pool used while running portlets through
their preRender Phase.
if the following are set 
forkRenderer uses renderQueue

IIRC -  if you do not configure a render or prerender queue the main weblogic
queue will be used.

--
Chris Jolley