Hi
If I understand you correctly you are trying to save the form with a specific name.xml in the same place but without overwriting it?
If this is the behaviour you desire then SharePoint would allow version control to allow the exactly same named file to save in the same place while still recording the old versions.
To force the name of the save file you could use code to SAVE with a specific name on a button such that you press the button it saves the form with the name specified in the code.
I hope this helps
Cheers