is it possible to showroom only certain categories?

is it possible to put on showroom mode only one or certain categories?

You haven't explained the "why" behind your question.

Simple answer: no. Not the way that you would put the whole store into showcase mode.

Better answer: yes, but not the way you're thinking.
If you create your products as Document-General instead of "Product-General" (from the pulldown list in your admin before you click "New Product" button), those products will not have an Add To Cart button, and thus cannot be purchased.
There is no built-in method for changing the product-type once a product is created.

And you REALLY need to upgrade your site to a more secure version. Your version has known security problems, which are fixed in newer versions.

i have a category with a lot of products which has been down for months. Before search engines forget it i need it to be searchable except making it possible for purchases. it will be up again.

"a category which has been down" ???
Please explain.

Because a supplier has been failing, the category for their products was disabled. Nothing wrong with zc. It will be enabled anytime of choosing.

You could simply set the products as out-of-stock and tell your store to not allow purchase of out-of-stock items.