Subsonic 3 SimpleRepository NON Plural Table names

It sounds like you already have a database designed in which case I would suggest you use the LinqTemplates or ActiveRecord instead. SimpleRepository seems to really be suited to a code first development process rather than a database first.

you need to get linq to populate it,
using something like
var query = from product in repo.All(Product)
join categoryItem in repo.All(Category)
on product.CategoryId equals categoryItem.Id
select new {
ID = product.ID,
name = product.name,
description = product.description,
categoryId= product.CategoryId
category = categoryItem
};