For audio: a good starting point is the rule of thirds: pull speakers 1/3 of the way into the room and 1/3 of the way from the side walls. You sit 1/3 of the way from the back wall with them toed in a bit to create an image in front of you.
If you search for "speaker placement" on one of the web search engines you will find the Cardis and other sites that go into more details.
Anthony,
I believe on Stereophile's Guide to Hometheater site they have a downloadable Excel spreadsheet that will calculate your nulls, etc. www.guidetohometheater.com
Patrick
------------------ My DVD Collection
Patrick The 69th most popular name for boys according to the Social Security Administration.