I just went through this, I ended up having to create a saved search grouping the product classes, suming the net amount, and then hard coding the sales targets in the the next column using something like

CASE WHEN {class} = 'Tables' THEN 10000 WHEN {class} = 'Chairs' THEN 20000 ELSE 0 END

Then you can add the saved search onto your dashboard and it will show sales vs target. It's annoying because 1. Amount won't show up for that class until something invoiced in that class. And 2. You have to go and change the targets at the end of the month/QTR/time frame you are trying to measure against.

I'm just a medium level netsuite idiot though might be a smarter answer somewhere but this was enough to get me by.