that is correct but it is based on what kind of xml file and how you want to populate it. If you are looking for a server side event then yes the LiveCycle suite would be needed. But this is not a straight forward thing to do. It is a great, powerful tool set but requires advanced knowledge and besides the license purchase will require development time to set up and to work with your process.
Thanks for your help! I spoke with someone at Adobe and it sounds like I need to purchase the server modules to get the form to pre-fill based on an xml file as well as posting to the server (sounds like what you're suggesting as well).
If there's a way to do this with just Livecycle, please let me know!
I am concerned about your first statement that the form is locked. If it is locked and depending on what security is applied you may not be able to edit it even with LiveCycle Designer if you do not have the password. In that case you may have to recreate the form from scratch.
-I want to be able to pre-fill the fields based on some external input (XML most likely)
Yes you can do this. You will need to map the fields to the sample XML or XML Schema
-I want to allow the user to modify the fields and click a button to send the data (XML) off to a web service (a dynamic URL that I want to set when the user launches the form).
Yes this is also doable however you will need to have the back end set up to accept the data. You would need to have a WebService that allows a data post.
-This web service will require some sort of authentication, so I'll need to pass that along too.
That would be included in how your WebService is set up. This is not an easy step and will require someone with the ability to create this WS.