What kind of techniques can I legally use to discover if a produc t really is violating some (L)GPL code ?

[Diamant-Berger, Antoine]

Hi,

My name is Antoine Diamant-Berger (French, living in France, so French Law
applies), and I follow closely a few open-source projects. 
This post concerns one of them, which is released under the LGPL.

We have found significant naming similarities in the DLLs installed by a
widely distributed commercial application and the dlls obtained by compiling
an older version of the project.
What kind of techniques may I legally use to discover if the commercial
application really is infringing on the project ?
What do you think our next step should be ?

Thanks.

Antoine Diamant-Berger