We have aluminum basment windows installed in metal framing that was installed during construction in a poured concrete basement. How to attach vinyl replacement windows into the steel framework?

I'm pretty sure you can't. A vinyl (or wood/vinyl) window set up comes with vinyl flanges to attach to the outside of the house. The sash-alone windows are designed for wood framing or for inserting into a smooth space with two liners on each side. I would imagine you have to remove the metal frames (are you sure they are steel?).
Or you could add a picture here.

You can install a wooden buck that attaches to the frame and then use a replacement window.