If you would like to display your subproducts in a pull down menu there are two areas in the product template that you would need to edit. The DEFINE SUBPRODUCT section of the product template and the DEFINE PRODUCT section of the product template.
Start by replacing the DEFINE SUBPRODUCT section in your product template with the following.
After you have setup the code for the DEFINE SUBPRODUCT section, you would need to include the LOOP SUBPRODUCT tags with the DEFINE PRODUCT section of your template where you would like the subproduct pull down menu to appear. The LOOP SUBPRODUCT tags would look similar to the following. Note that this code needs to be within your add to cart form (see product add to cart) so that the product selected in the pull down menu gets added to the cart. You do not need to include the <input type="hidden" name="itemnum" value="[-- PRODUCT.RecordNumber --]"> which is part of the add to cart form.