installation of what ? your question is a bit vague.
In general, you would locate the registry key for a product by a) documentation or b) a registry editor tool - once you know the location of the 'installation' from the registry which is a 'key', you would use Registry.GetValue() or such to get the data, supplying the right 'key'
There's examples here (quick googling would have found this) :-
This article right here in CP may also help :-
Working with Windows Registry using VB.NET