Google Indexing Pages That Don't Exist

[poolgod]

I am having a problem and maybe someone can help me determine the best course of action.

On our site we have a products page that is dynamic, googlebot seems to be programatically going through each product page id number looking for content. The problem is that there are categories for products that contain nothing. Google is finding them and indexing those pages even though they are essentially empty. I want to stop googlebot from indexing those pages at this time, but leave open the possibilty for it to index them in the future when there are products in them.

The site is built using ASP so I thought maybe setting up a response 403 or something would do it.

Thanks for any input.

-PoolGod