While it is possible to use the netboot cart with a 'standard' TFTP server, you lose a lot of functionality. The biggest is, standard TFTP servers do not allow a TFTP client to request a listing of available files, they only allow a client to request a file with a specific name.
So I made an 'extended' TFTP server in ruby (bin/tftp_server.rb in the netboot zip file). To use it, you need to install ruby first (e.g. from
http://rubyinstaller.org/ )
When the netboot.bin cart image starts, it first tries to download a list of available files which will only succeed if you are running the tftp_server that came in the zip file. If that request fails, it then tries to download a file with the fixed name of "bootc64.prg". So if you want to use a 'standard' tftp server, you will need to rename the file you want loaded on the c64 to be "bootc64.prg" and put it in whatever directory the TFTP server looks for files in.