Interxion has a partnership with Equinix:
http://www.interxion.com/cms3000/modules/content_pages/page_preview
.asp?Page_id=38&NodeID=A_128&navID=2
Both companies were established in a similar timeframe (1998),
raised similar amounts of money and have similar services/products.
fyi: Interxion has the largest carrier neutral datacentre
footprint in Europe & is one of the few datacentre companies with
really good power engineering standards; note that I am slightly
biased in this matter.
Regards,