[Magus]

As far as I know about removing paint with sandpaper, if its plastic that have been painted, with sandpaper... you cant do a thing about it, if you take the sand paper too rough (like 150-200) it'll leave some pretty nasty marking, but if you use sandpaper thats too fine (400 and more), it will just get dirty and wont be able to sand anything very VERY fast.

You may be able to do something with paint thinner, but i don't know enough about it to give you any advice that would be usefull.

If its metal that has been painted, you MAY be able to work something out, by using some metal grade fine and very fine sandpaper, but even after that, you'll need to do a polishing job. And the best way to do it is by using a cotton wheel (i don't actually know how its called) and, depending on the ''toughness'' of your metal part, some polishing paste.

But if there is a lot marking or ''parts'' fixed on what you want to sand (like a rail) you wont be able to do anything good and it will end up looking like if you did a dry brush job on it, leaving paints in the ''deepest'' parts and with the ''top'' parts clean.