Im with ct...booleans are great...but it takes planing and cleaning if the geo is complicated or smooth. If it was me...I would split poly to roughly the shape, then I would select faces and delete, then extrude etc to replace...and edge loop etc. It sounds like hard work but it can also be much less tedious and messy and you will have much more control over your geo.
Cheers bullet
bullet1968
"A Darkness at Sethanon", a book I aspire to model some of the charcters and scenes