I want to conditionally auto-populate a summary worksheet
 

I want to make a worksheet that will summarize the data from two
spreadsheets, called "cars" and "parts", which have three columns
each, one for description, one for SKU, and one for quantity.

I'm trying to make a third worksheet display only those rows with a
quantity of greater than 0. I want to split the third summary worksheet
into two vertically split sections, one for cars, one for parts. I need
to subtotal the "parts" and subtotal the "cars" sections, and then make
a grand total.

I want this to be a dynamic worksheet, so if you change the quantity of
a line item in "cars" or "parts", it will automatically show up
in the third summary worksheet.

Please help! This has been driving me nuts for a while now.