Here's a great link
http://www.sheldonbrown.com/singlespeed.html.
I ride a singlespeed specific bike so I can't help too much with conversion info but here's what i've seen. there seems to be different levels of SS addiction. It starts by removing the extra gears and shifters off your geared bike and adding a tensioner, like the surly singulator. The next step is adding a SS specific rear wheel. and then finally stepping up to a SS specific bike or frame.
My opinion is that if you want to see if you'll like SS convert your current bike as cheaply as possible or even just ride in one gear for awhile. If you already know that you like singlespeed you'll probably be better off in the long run to sell your current ride and step up to a SS specific bike.
I bought my Bianchi BaSS used with some nice upgrades for a little over half of what it sold for new.