Need help in designing mastar detail form (Sales Invoice)

Question

Hi I need help regarding designing a simple sales invoice form in desktop application..

I have to make a sales invoice. i have fields like invoiceNo, custname, invoicedate,TotalAmount in my salesinvmast table. And ItemCode,ItemName,Qty,Rate,Tax Amount in my salesinvdet table.

Now i want to design a simple invoice form so that i can have mast table fields on top and in bottem half i need textboxes and combo box using which i can save the item details on data grid. and finally using savebill button i am saving the whole bill. My problem is what is i have an item who has some sub items like an item are in different packaging format like say 1liter, 2 liter and 5 liter.  how can i make possible to select from the list of this packaging type.

One suggest i feel is when i select an item and suppose the company name the a popup of these packaging items should come up on "textbox1_leave" event, and after selecting one of the thing it should get back to main grid.

I need some suggestions about making this form a better way.. Plz tell me how can i post image here of my form so i can show how i did as i am new to this forum.

Then you can get idea about how i did and what i exactly want.

Thanks in Advance.