The correct way to add Variants to WP e-Commerce is as follows:
First click on Products > Variations.
Name the fist something like “SIZE”, then scroll down and click on “Add
New Variation”.
Next enter something like “COLOR”, then scroll down and click on “Add
New Variation”.
Next, one at a time enter sizes, and colors, NOTE, make sure to have “Variant Set” set to the proper type (Color or Size), followed by clicking on the “Add New Variation” button.
On the right side of the screen you should see a tree of COLOR, and SIZE, each with sub variants.
Then go to “Add New” and enter a name like “Shirt”.
Next scroll down to add the variations you wish to use by clicking on the correct boxes. NOTE you may have to save (update) the post once before you are able to add variations.
Last click on “UPDATE” and you should then be able to view your product, and its variations.
NOTE: Anytime variations are revised or added, the product may also require updating.
It this still does not work, please reply.