Welcome to the Shack! There are many ways of accomplishing a HT sub. From sealed to ported to infinite baffle. Big, small, and average output up to the extreme. If you could tell us what your expectations are in sub output and what your budget is, it would be a good start. To get your feet wet, you can download WinISD, a modelling program, and play around with different sub designs.
http://www.hometheatershack.com/foru...30-winisd.html
Another good program is UniBox.
http://www.hometheatershack.com/foru...31-unibox.html
And to help you understand what the parameters mean.
http://www.hometheatershack.com/foru...arameters.html
If you have any questions, just ask.