PuTTY

PuTTY is a free implementation of telnet, ssh and terminal emulation by Simon Tatham. It seems to be the preferred way to play NetHack on a public server on Windows, as it is much more versatile and standards-compliant than Microsoft's telnet.exe that comes with Windows.

PuTTY can be downloaded from PuTTY homepage

To make IBMgraphics work with PuTTY, you need to set Window/Translation/Character Set to CP437