ps. If you want do dive into that course by Dan Kennedy that Steve mentioned above, get in touch privately and I'll set you up with a discounted copy.
That being said, there's an entire (and great) section on speaking, how to market yourself as a speaker etc in the Back-end Marketing and Joint Ventures course that Dan did... it's currently the upsell to the same offer Jason Moffatt talks about here: http://www.jasonmoffatt.com/internet...nd-losers.html
Though I'm obviously biased, Dan's materials really are worth studying. But, again, first you might just want to make sure you lock down an EFFECTIVE presentation and have a product/offer that is high value, high conversions that you can sell.
OH, and if you REALLY want to play the speaker circuit game, eventually I'd recommend you release a book. Which really is no big deal these days. It's like a long ebook, that you then give to some outsourced labour, they format it and proof-read it and get it in published book format. You buy a ISBN number and get it onto Amazon.com . Voila! Now you're a published author.
But to most people, a physical book means you're a big deal. The credibility points you score from that will land you more speaking gigs but even at the seminars, you'll close more sales because the audience too will view you as a high authority.