How to Add Row to subform via script?

How to Add Row to subform via script?

Hi,
 
I have a bunch of itesm in the multiselect checkboxeds
 
eg:
 


 

Thes are actually len x width based pricing
When the item is selcted in thse checkboxes, i would like to add a row to the subform and pre-fill it with the above values
 
len = 1 ; wid = 24 ; unit proce = 4.9
 
So that, in the end, the user only enters  the (No. of items) in the subform, ... This is to mimise manual error
 
I have set the default row = 1 in parent form & input the selected values in the appropriate fields
But t works only if one item is selected.
 
When multiple items are selected ,  this does not work
ie, when the user selects all 3 items, I would expect to see three rows in the subform, with pre-filled len / wid / unitprice.
 
 
Any help is great help
Thanks in advance
-Deepa Govind
http://homepreneur-online.com/