It depends...
1) Submit from browser, or on the user's desktop as an XML, but without the need to save the data locally - don't need reader extensions.
2) Submit from browser, or on the user's desktop as an XDP or PDF, with or without the need to save the data locally - need reader extensions.
3) Submit from browser, or on the user's desktop as an xml with the need to save the data locally - need reader extensions.
Note, if you do not have a need to prepopulate the data, and the data is coming in as direct XML, you dont even need form server.
David
www.ensemble.com