Plenum removal may be required for several reasons, such as camcover gaskets replacing, cambelt replacement or cam timing.
The guide describing the plenum removal can be found here:
Removing V6 plenumhttp://www.omegaowners.com/forum/index.php?topic=90657.0Essentially the plenum removal instructions for the 2.5 & 3.0 engines are still valid, but the newer 2.6 & 3.2 engines are slightly easier to work on due to the fact that there are fewer components to remove, e.g. no ICV, EGR, or HT leads.
If you have one of the newer engines, you might find it easier to follow the instructions below for plenum removal and then proceed with the 2.5 & 3.0 guides for the operation you intend to carry out:
Changing the V6 Cam Cover Gasketshttp://www.omegaowners.com/forum/index.php?topic=90542.0
V6 Cambelt changehttp://www.omegaowners.com/forum/index.php?topic=90518.0