Data Shaping, Horizontal Loop and SQL statement

I am currently building a website and I need to have a horizontal loop from a Data Shape Recordset which also filter the records from a category table. So I have 3 tables. One is a ProductsMain table which carries the product name, description and the paths for the images. I have another table entitled ProductsSizePrice which holds the size, price and product id. Many of the products come in several sizes so I have put them in a separate table. Also I will aventually have an Add To Cart button for each size of a particular product, so these need to stay in a separate table. The third table is ProductsCategory and this holds the categories which each product falls into. It is in a separate table because some products fall into more than 1 category and I do not want to have to repeat the products in the ProductsMain table. I have used data shaping to successfully pull all the products from the ProductsMain table and all the sizes for each product under each product. So I have a loop within a loop. My problem is I am not sure how to add the Where clause into this to only select from a certain category from the category table. Also I am not sure how to make the repeat region become a horizontal/vertical repeat region at the moment it is just a vertical repeat region and repeats all the way down the screen. I would like it to go 4 accross and then onto the next row. So in short I need my data shape loop made horizontal and my where clause to filter from the cateogry table.