If you use the POST method there is virtually no limit, although the server may think differently (memory issues etc). 200 parameters should not be a huge problem though.
If you use the GET method you're going to have a problem. Most browsers only allow a limited length of the URL they request. Since GET puts all parameters in the URL that URL can be quite long. If the maximum length is exceeded (and for Internet Explorer this is quite small, 1024 or something like that) then the browser can send a part of the URL for the request, or more likely not send any request at all. IE shows the latter behaviour - I got annoyed by that myself.