[jQuery] JSON MIME type?

[jQuery] JSON MIME type?

I'm using the jQuery Form plugin to call an <a href="http://ASP.NET">ASP.NET</a> 2.0 page.  The call works just fine, but the response never comes back right.  If the Response.ContentType is set to "text/plain" the page gets forwarded to a plain text JSON result.  If the
Response.ContentType is set to "application/json" the browser attempts to download my aspx page.  All I want is for the result to be forwarded to the success event handler.  Could it be the content type parameter, or is there more going on here that I haven't seen?  I can post code if necessary.
Thanks,
MR