Wordpress Google checkout Integration

I wish to develop a simple Wordpress shopping cart with checkout using Google checkout. A post in Wordpress is designated as an item utilizing custom field key and values. 1. is_item=yes 2. color_attr=red;green;yellow 3. size_attr=12E;13C;14B 4. vendor=zappos 5. vendor_ship=12 6. item_ship=2 7. qty_avail= -any key with the _attr (up to 3) will display a pull down in the item post. -the vendor is used as part of the shipping calculation which is simply; if from the same vendor its vendor_ship (once) + item_ship (for each item) -qty_avail is used for the quantity order input box in the post. If blank show a blank input box, if a number show number available. Plugin setup required -Google assigns you a unique identifier called a Merchant ID -specify a range of zip codes in a tax input field by using an asterisk as a wild card character. The process begins when the buyer puts items in the cart and is ready to check out. In Wordpress a small Ajax widget lists the cart contents in the sidebar. We will specify merchant-calculated shipping price which Google asks through the api to calculate the rate as described above in vendor_ship and item_ship Payment terms are three equal payments 30%/60%/100% completion.