The general approach to this is to use a so-called "unbound" form and issue the needed insert/update by code.
Personally I don't see the point of not using subforms, as that's easier and when using a "single form" view and no borders, the users won't be able to tell that there are subforms used.
I also suspect that you're trying to store "redundant" data, as this type of Q often "hides" the storing of totals in separate tables. Such an approach is "not done" in a real well designed database.
For more info you'll need to supply us with more information...
Nic;o)