if you are directing your users to an internal help desk web page you can use a tool like nbtscan and a little bit of perl cgi to do this for you.
Something like this should work and output what you need to a file.
$ip = $ENV{'REMOTE_ADDR'};
$command = "/path/to/tool/nbtscan -v -h -q -s "$ip"";
open(FH, ">>filename")
or die "error creating or opening file: $!\n";
# Print outtput to file.
$tm = localtime;
print FH "Record added : $tm\n\n";
open (S, "$command |") || die "Cannot run $command! : $!\n";
while (<S>){
print FH $_;
}
close(FH);
The environment variable REMOTE_ADDR will get the user's IP address for you. feed that to the tool and it should give you the data that you need.
This might be limited by your routing topology as the server will need to directly connect to the machines using the tool.
Not sure what DHCP server you're using but that should hold MAC to IP mappings too.
Network Pen Testing : Tomcat authentication with sqlmap
