I would probably use paint stripper to get rid of most of the paint and then sand it.
If the chipboard was not sealed prior to the black paint being applied, there is a risk that the paint has 'soaked' into the chipboard. That means a *lot* of sanding - I'd paint it with brown paint, if that is the case.
If it sands down ok, then choose your stain, read directions and apply.
Depending on the chipboard's use, I would probably use a stain/clear combination.
Some tips here:- http://wood.wattyl.com.au/tips/techniques.cfm
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