you can uncompress it from the command line. in the terminal go to the directory you downloaded the PublicBeta_Developer.tgz file into. type the following with out the quotes-
"tar -xzvf PublicBeta_Developer.tgz"
or
"gunzip PublicBeta_Developer.tgz | gnutar -xvf -"
from what i understand the version of expander that comes with os x has a bug when decoding tar files. you can uncompress it from the command line however. in the terminal go to the directory you downloaded the PublicBeta_Developer.tgz file into. type the following with out the quotes- "gunzip...
it runs in the terminal so to start it up you need to navigate to the directory it is in. then type "./dnetc"
works fine for me on an new ibook se and an imac.