You "should" already have Ndisasm. If you downloaded a "package", ndisasm.exe should have been included. If you built Nasm from source (which is the way I do it), "make install_everything" should get you ndisasm, documentation (in more formats than you can shake a stick at), plus some rdoff utilities that you probably don't want. Ndisasm has always "come with" Nasm - even in the versions where the documentation had gone missing.
They're built from the same source (mostly).
However... you may be disappointed in it. While it is true that it's in Nasm syntax, the format is not suitable for reassembly, as is. Worse, it attempts to disassemble everything - headers, data and all - which may result in trying to disassemble half-way through an opcode. This can all be fixed by telling ndisasm "start here", "stop here", "synch here" on the command line (I never found that "intellegent synch" worked very well), but it's a royal PITA.
Instead, I suggest you take a look at Agner Fog's "objconv". The "-fnasm" (no space) option produces a disassembly in Nasm syntax which is (IMO) much nicer than what ndisasm gives. "objconv" does understand object - linkable or executable - formats (that's its job), where ndisasm doesn't even attempt to.
http://www.agner.org/optimize/#objconvCheck it out!
Best,
Frank
