You are looking for the AJAX object. It allows GET and POST requests:
In my experience, there are 2 gotchas:
1. Remember to properly escape any quotes "".
2. The format for sending POST data is the same as for GET. In the C2 manual it says:
[quote:2grndpef]Post to URL
Send a request with data to a URL and retrieve the response. A tag is provided to match it up with the On completed, On progress and On error triggers. Construct 2 does not automatically URL encode the post data - use the URLEncode system expression to ensure the data is in the correct format for posting. Note post data is in the same format as a query string, e.g. "foo=1&bar=2". The method can also be specified: by default it is POST, but for some APIs you may need to change this to PUT, DELETE or another HTTP method.