Hi,

> Does someone know of an "open" molecule structure search on the net ?

Try the COD (Crystallography Open Database) at :
http://www.crystallography.net/
However, that very young database contains only ~15000 entries
instead of the known ~400000... The number of organic and
organometallic entries is rather small. Up to you to add your
own atomic coordinates. There is also a growing subset
of predicted inorganic crystal structures.

Armel Le Bail