Send and Receive XML

Hi, I'm not really sure if this is the right list to be sending this to, but I have a few questions about how to send and receive XML files and don't know where else to write to. We are implementing a B2B solution between my company and another and I would like to do all the data transfer using XML, rather than some proprietary file format. The other company will be using VB on client PC and I'm using PHP and C++ on a unix web server. How would the PHP receive the XML? Perhaps I'm doing this all wrong. Maybe I should just be going back to good old TCP sockets and just send and receive data a particular port. I envisiged that somehow the VB application will make a HTTP request to my PHP page through the web server and somehow with some magic, send me the XML file. I have heard that to send an file, you place the file in the HTTP Headers? Is that correct? Anyone got any idea of where I can get help on this sort of thing? Thanks, Sam