managing categories and brands

Are you pretty comfortable with ASP and SQL?
If so, then try sites like http://msdn2.microsoft.com/en-us/library/bb264565.aspx.
If not, try http://www.w3schools.com/default.asp for tutorials on many subjects related to web design included ASP and SQL. If you do a search on "writing SQL queries" you'll find a bunch of sites.

Anyway, the basics of what you'll need to do are as follows. (Please note, this should be one long string but I split it into different lines for readability):

SELECT idBrand,BrandName,BrandLogo 
FROM Brands 
WHERE idBrand IN (SELECT DISTINCT IDBrand FROM products INNER JOIN categories_products ON products.idProduct = categories_products.idProduct WHERE (categories_products.idCategory = idCategory) AND (products.active = - 1) AND (products.configOnly = 0) AND (products.removed = 0))
ORDER BY BrandName ASC;

The "WHERE idBrand IN (...)" statement basically gets a unique list of the Brand IDs for the products in a specific category. You will need to change the section that says:

categories_products.idCategory = idCategory

by changing "= idCategory" to the actual category you are working with in viewCategories.

Then the main query retrieves the brand info for brands with the BrandIDs for the products in the selected category.

Hope this gives you a good starting point. If you still can't figure it out, you could hire one of the Product Cart developers. (We are one but there are others.)