UPnP and DLNA are two different standards.
DLNA is derived from UPnP, as an attempt to normalize media interoperability. It does this partly by being more restrictive than UPnP (e.g. by restricting the number of media formats) and partly by adding features (like DRM, i.e. copy protection).
DLNA guidelines can be thought of as
an umbrella standard that defines how
the home network interoperates at all
From the DLNA whitepaper (pdf).
The UPnP A/V spec provided a strong
and flexible means to share content
throughout the home, but because UPnP
offered rather overwhelming
flexibility in the choices vendors and
providers could make in configuring
their products and services, (push vs.
pull, what types of video and audio
file formats have to be supported,
etc.) the DLNA developed its own
interoperability guidelines to
simplify the process.
I couldn't find a clear answer on whether pure UPnP and pure DLNA devices are directly interoperable today, but in 2006 they weren't (pdf). My bet would be "probably not", unless at least one of the devices can handle both.