Data Binding Question.

I have a problem that I jave been struggling with for several days...

I have a form with a three text boxes that are bound to a dataview like:

this.Quantity.DataBindings.Add("Text",DataSet1.Table1.DefaultView,"Quantity");
this.UnitPrice.DataBindings.Add("Text",DataSet1.Table1.DefaultView,"UnitPrice");
this.Subtotal.DataBindings.Add("Text",DataSet1.Table1.DefaultView,"Subtotal");

I'm working with a legacy database, so I need to actually write the subtotal
to the database, instead of using a calculated field or column.

I have been trying to get the Subtotal textbox to calculate the correct
amount as soon as the user changes the Quantity or the UnitPrice values.

The closest I ever got was using a CurrencyManager object, but the Subtotal
only refreshed when I moved forward and then back in the dataset. I just
can't get it to update otherwise.

Can someone help me with this. I have combed through the newsgroups and I
found several "close" examples, but none have worked so far.

Any help will be greatly appreciated.

Thanks.