Have the same problem - running windows 8.1 pro, and used the windows NVM manager to install Node v 4.2.0
Looks like a problem in the install package - as the node error is suggesting.
C:\Users\myuser\AppData\Roaming\nvm\v4.2.0>npm install -g bitcore
firstname.lastname@example.org preinstall C:\Users\myuser\AppData\Roaming\nvm\v4.2.0\node_modules\bitcore\node_modules\bitcore-nod
'.' is not recognized as an internal or external command,
operable program or batch file.
npm ERR! Windows_NT 6.3.9600
npm ERR! argv "C:\Users\myuser\AppData\Roaming\nvm\v4.2.0\node.exe" "C:\Users\myuser\AppData\Roaming\nv
m\v4.2.0\node_modules\npm\bin\npm-cli.js" "install" "-g" "bitcore"
npm ERR! node v4.2.0
npm ERR! npm v2.14.7
npm ERR! code ELIFECYCLE
npm ERR! email@example.com preinstall:
npm ERR! Exit status 1
npm ERR! Failed at the firstname.lastname@example.org preinstall script './scripts/download'.
npm ERR! This is most likely a problem with the bitcore-node package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR! ./scripts/download
npm ERR! You can get their info via:
npm ERR! npm owner ls bitcore-node
npm ERR! There is likely additional logging output above.
npm ERR! Please include the following file with any support request:
npm ERR! C:\Users\myuser\AppData\Roaming\nvm\v4.2.0\npm-debug.log