You can use the beforeInsert() trigger:
http://framework.weblite.ca/documentation/tutorial/getting_started/triggersNote.. I recommend you read at least the first 5 or 6 sections of the getting started tutorial if you want to start building with dataface. It doesn't take too long and it should give you some good background on what you need to do.
e.g.:
function beforeInsert(&$record){
$record->setValue('username', 'some username');
}
or even better
function beforeInsert(&$record){
$auth =& Dataface_AuthenticationTool::getInstance();
$user =& $auth->getLoggedInUser();
if ( $user ){
$record->setValue('username', $user->val('username'));
}
}
For the timestamp, you can either use a MySQL timestamp field to have mysql do it for you automatically, or you can use a datetime field and use the 'timestamp' directive in the fields.ini file.
e.g.
[mydatefield]
timestamp=insert
or
[mydatefield]
timestamp=update
-Steve