Submitting survey via AJAX

Has anyone had any success doing this? I'm working on an application that is, effectively, signup mechanism -- not for our site/email list, but rather an event of sorts. Not an RSVP though and one that simply wouldn't be appropriate for the Convio Event application. Point is, its on our site rather than in Convio (because we need some custom code that we can't do on Convio's server) and using the survey tool to provide an easy reporting interface (aka, a single file) to the group that's running this event and I'd like to use AJAX to submit the form because it makes for a better experience, etc. Anyway, I'm having trouble with it and I can't figure out why.

When I submit the form directly, that is, WITHOUT using AJAX, it submits fine but when I use AJAX (and pass everything through a server-side proxy) it seems to fall down... Is there some particular limitation with Survey's that prevents it from taking survey input from external hosts?

(sorry, I can't provide a link, it's all on our internal dev server right now and not accessible externally)

Thanks!

-mike