Installing Drawer Sliders?

I am trying to repair a kitchen drawer. It needs new slides. I just got done repairing so nicely and when I went to insert the drawer, it wouldn't fit with the new slides. I wanted to use side slides, not the middle thing that is in there now. And yes, I remembered the "measure twice, cut once rule", although I didn't cut anything.

Any hints as to how to accomplish this and keep my sanity and salvation? Can I use side slides or am I stuck with the middle thing (pardon the technical terms). Can't afford new cupboards, What I would spend on new cupboards will buy a couple of tanks of gas. : )

Mrsmendlebright from Kearney, NE