The public development hub has now changed address. It is now adc://dcdev.no-ip.org:16591. This means that you need to run a client that support ADC.
The following clients support (atleast partly) ADC;
DC++ - http://sourceforge.net/projects/dcplusplus
Elise - http://sourceforge.net/projects/elise
JDC - http://sourceforge.net/projects/jdc
FMDC - http://flow84.no-ip.org/fmdc/
It will not be a NMDC hub ever again. It is time we move forward.