Hello,
Things you need if you are running PPC to an ecommerce site to achieve the maximum ROI.
1. Keywords need to be very tightly focused on your product. Adgroups should not have more than 4-5 keywords max in them. You might even want one keyword per adgroup. DO NOT: bid on keywords like "laptop computers" "buy computer". Your keywords need to be specific computer models, and drive them to the specific page where they can buy that computer. Also, calls to actions need to be very clear. Have you tested different landing pages. This increases conversion rate dramatically.
2. Are you using the content Network? You can go broader with the content network than search. Lets say you have a page full of refurbished dell computers. You can drive content traffic there by creating an adgroup of around 50 or more keywords all themed around refurbished dell computers.
Just to let you know, I'm a certified adwords professional, live in the US and manage over 50 clients in both Google and Yahoo at an interactive agency. That's over 100 accounts I'm responsible for. I've consulted Estee Lauder, and have built many campaigns for B-B and B-C companies.
Contact me if you want a professional to handle this project.