This is really part 2 of a 2 part tutorial on scraping configurable product data, which began here. For those people not interested in the scraping aspect of this project, you can download the magento sample data here. Warning, this sample data might be NSFW if you have an uptight boss.
The first thing we're going to need to do is set up our categories. Open the products spreadsheet in Excel or something similar and Highlight the _category column (column L) and copy that. Bring that into a text editor and sort the values / remove duplicates. Each unique needs to be a category in Magento or you will get an import error. When you create the the categories, set them to 'Enabled' so they show up in your storefront. Drag all your categories into the "Default Category" root category after you make them.
Next we need to set up the attributes. Copy columns _super_attribute_code and _super_attribute_option (S and T) into your text editor and sort/remove duplicates. You'll see unique values for 2 attributes, color and size. These both need to be set up in Magento.
So go to Catalog / Attributes/ Manage Attributes, create a new color attribute if it doesn't exist and set:
Scope - Global
Catalog Input Type for Store Owner - Dropdown
Use To Create Configurable Product - Yes
Next click on Manage Label / Options and add your color options. Then do the same for size.
Now you're all set for a clean import. Head over to System - Import / Export - Import, select Products, and upload the spreadsheet. If you are using Magent Go you can import the Product Images in the same way. Otherwise you'll want to ftp those to your media folder.