I use a program called Room Equalization Wizard, which can be found, as well as much helpful information here:

http://www.hometheatershack.com/roomeq/wizardhelp/help_en-GB/html/index.html

then the use of a SPL meter from Radioshack is what collects the information.

By the way, welcome neon! and let me know if you have any other questions I can answer in regards to REW. I've been slaving over it for a few weeks now and feel like I have a decent grip on it.

Steve