Not sure if this is exactly what you're looking for, but here's how I do dataset updates from code:
Code:
dsDataSet.Tables("TableName").Rows.Find("KeyField").BeginEdit()
dsDataSet.Tables("TableName").Rows.Find("KeyField").Item("ItemToChange") = "SomeValue"
dsDataSet.Tables("TableName").Rows.Find("KeyField").EndEdit()
dsDataSet.Tables("TableName").Rows.Find("KeyField").AcceptChanges()
Sounds like you want to update values in a record -after- the user has inserted that record? Depending on how your data source is defined the syntax may not be exactly right, but I happened to use this a little while ago on a project I'm working on. I'm pretty green so there is probably a better way to do this but it seems to work fine for my purposes.
If you want to do it before the record gets inserted I guess you could watch for a .CurrentCellChanged event but I don't think I'd do it that way (but what do I know heh)
Hope this helps.