Create custom XML file from a wordpress form

[spymode]

I am building a WordPress website which would be need to integrate with an in-house CMS system through a simple custom XML file.The client would like the users to submit a form in the WP website, and the form will send an email and will save on the server an XML file with a specific structure.Is there any form plugin for WP which save an XML file on the server with form's details?If not - is there any form plugin with custom JS (to write the code myself)?Thanks for all the answers...