First question: Do OMSPs work as that object?
Example: If I use a table OMSP and nothing else, does it act as a table.

Second question: Are there desk OMSPs?

The reason for my questions is that I want to put a computer on an object that is not a desk, but I want it to act as one.

I don't believe OMSPs alone generally act as anything in particular except a table, since I imagine they're mostly cloned from one-slot end tables. That said, there is one that acts as a kitchen counter, so that Sims can prepare food anywhere, like on a kitchen table, but I've never seen one that adds desk functionality.

On the other hand, you can put a computer on a dining table without any OMSPs and the Sims can interact with it just fine. You just can't stick computers on endtables or coffee tables because the Sim can't sit in a chair next to such tables.

I haven't seen one which adds desk functions either, but you could try looking for an invisible recolour of a one tile desk and position it so that it looks as though the computer is on the item? The only thing is it will have to be the right height because otherwise the animations wouldn't line up properly. You could put the other item on the OMSP if it's blocking the chair from pushing in.

For that to work, wouldn't you have to put the table on the OMSP? I don't think you can put tables on an OMSP. Then again, I've never tried...

I've also never seen invisible desk recolors, but if it'd work, that might be a handy thing to have although, like you said, most non-dining tables aren't the same height as a desk so the animations would be wonky.

In SIlentLucidity's first omsp set there are "functional" omsps: desk, counter, and I forget what else. Anyway, it's right here: http://www.modthesims.info/download.php?t=317716

You can put any one-tile object onto the black OMSP, supposedly. But as said before, if you want to use a table then just use a table. It's if you want to use a deco object or something that you'd need an invisible desk.

Lucy: That link does not contain a desk OMSP.

Now I want to put a computer on an OMSP, turn it invisible, and have a sim use a computer floating in midair.

Laughing - I want to see that pic

Aha, thank you for the answers everyone. Definitely helped a lot.