How are you displaying it? Usually you would use a relational table if one product could be in multiple categories... so you would have:
Products contains: ID, Name and etc... (notice no CatID)
Categories contains: ID, Name
ProductCategories contains: ProdID, CatID
So that if the ProductCategories table had two rows:
Then productID 1 would be in both category 1 and category 2... that way you can use inner joins to relate the three tables.
It is possible to do it with two tables as you mention, but you would have to depend on LIKE searches and couldn't use standard SQL joins.