Can anyone point me in the right direction to find information on subwoofer crossovers?  At some point in the near future I'd like to build a subwoofer for my audio setup which probably will pull double duty as a HT.

I know next to nothing about crossover designs.  I recently saw a reference to a circuit called the Linkwitz, did a little reading over at ESP.  The circuit looked particularly promising for HT as it boosts the very low end.  Looks like it'd be great for HT effects.

http://sound.westhost.com/project71.htm

While we're at it, I had been thinking about building a better sub for my little multimedia computer speakers.  Small size is desired, but small size means crappy low end.  If a long excursion suitable woofer could be found in a small size...could the linkwitz crossover be used here?  Obviously I'd like to boost just the low end of the audio, to get better performance down to around 40Hz.  I know it can be done.  Has anybody here done it or read about it?