Pass data from form to external URL via a Web Service call

I need to create a form that collects data and then will pass it on to this Web Service
https://weblogin.newbenefits.com/WLAuthNET/WLAuthNET.asmx (only using the CreditCharge call)

I have started creating the form http://www.fundraisingmidwest.com/?gf_page=preview&id=9
but need to figure out how to pass the data.

I am still new to web service calls and have been researching, it seems that it can be accomplished using Gravity Forms but the best approach is where I am stuck.

I came across this post http://www.gravityhelp.com/forums/topic/cant-find-any-instructions-to-post-form-data-to-external-url which is helpful but I am still learning all of this and have some questions:

I think I will need to create additional PHP to POST the data. But I might be making it more complicated. Would it be possible to just use the Confirmation redirect?

I have also read another post on using a before Submission Hook. It will be collecting credit card information which I really do not want them stored on my site I would rather it just be passed through.

Thoughts? Your help is greatly appreciated!

Yes, I did look at that post also. So if I am understanding it correctly it would look like:

'first_name' => $entry['1.3'], - the 1.3 is the input name of the field on the form?

Would I replace this:
$response = $request->post($post_url, array('body' => $body));

with: $response = $request->post($post_url, array('CreditCharge' => $body));

this is what I created to test http://pastie.org/5336518.js

when I inserted into my functions.php, I get an error

It is working now, thanks.

How would I add the entry ID to this code to send as a unique invoice number. After reading some post on creating unique number is seems that would be easiest.

I figured out another way to approach this by using the product fielid instead. Thanks for your hellp!