I was the one who built it and though I can't share all of the code, I'll try to give you some direction to get started. Both APIs are pretty easy to work with, so if you've got someone who knows their way around code, it shouldn't be a big deal.
Essentially, what I did was create a custom confirmation page for after an Eventbrite registration (you can set the custom page in the event's settings). On that page, PHP code would query the Eventbrite API for the event's attendees and find the new one. It would put all the pertinent details you get from the registration into variables, then it would call up the Marketo API. First it would query the email address against Marketo to see if the lead exists, if it doesn't, it would create it. Then, it add the lead to the corresponding event program within Marketo, where all of my smart campaigns take care of the rest.
Here's where to get started with the Eventbrite API:
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http://developer.eventbrite.com/docs/getting-started/
And the Marketo API pages of note:
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http://developers.marketo.com/documentation/soap/
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http://developers.marketo.com/documentation/soap/synclead/
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http://developers.marketo.com/documentation/soap/requestcampaign/
There's sample code for pretty much all of these that you can just grab and modify to get working. I can probably answer some questions if you run into any problems. Good luck.