could be oxidization, could just be dirt and grime that accumulates over the years. If its dirt, Yes, you can clean it with normal cleaning agents. In case of oxidization you need to use some more aggressive methods (like sandpaper, for example) and there will most likely be permanent damage from it.

I suggest using 90%+ concentration Isopropyl Alcohol. That tends to clean up gunk and can help with some light corrosion.

If it's really bad corrosion or rust, you have to follow what Koltoroc says.

furan wrote:

What is it that makes the metal frame inside of computer cases all course and gritty as opposed to when it was new? Is the metal oxidizing? Is there any way to clean this crap off so it's "clean?"

if it looks like the surface chipped away leaving a brownish rust looking texture it's good ole oxidization, just like a car one little spot of rust or tiny little chip in the surface will turn into a huge area of rust over so many years.

I like to scrub it with alcohol, very lightly sand the rest away if necessary, clean again, then spray with metallic rustoleum spray paint.. I've restored a few things that were almost completely chewed through with battery corrosion that way..

if it is on a bottom part and it is rusty you can sandpaper(rough grid to smoother grid) and/or give it a bath in vinegar (on the affected area only).
But if the bare metal is left exposed it will be oxidized again so i recommend after the treatment of the affected area that you apply some clear coat to prevent rust.
I bought several cards that had the bracket with tiny rust spots and i left in the vinegar for 24h and after that i scrubbed it with baking soda(to neutralize the vinegar and polish a little bit) and i applied two layers of clear coat and it looks almost a brand new
If you can give the 90%+ Isopropyl Alcohol a go first, if it don't remove the corrosion then i recommend you more agressive steps.