If you don't want to display the form, but direct the user to another script entirely, then you should output a 302 HTTP status code and a suitable Location header thus having them bypass (from their point of view) the page entirely. The drawback to this approach is that it adds a little to the complexity of getting any unchanging form data (that you would normally put in a hidden input) to the next script in the sequence.

If you have only a little data, you could encode it as a query string on the URI. This has the drawback of being bookmarkable and easily refreshable - which could have drawbacks if the submission changes anything on the server. (I'm assuming it will since you are using the post method in the first place).

If you have more data, or for a bit more safety, you could store the data somewhere on the server (a database or flat file) with a unique identifier, then include that identifier in the query string. (And have sensible clean up routines).