W2k DNS and internal Unix server

I have one W2k+ISA server; behind this ( are W2kWEB and mailserver, internal web server, 2 another w2k server, etc this works fine) but i have too one Unix server – wth with web service, etc – under another IP address-pool.
This is unavaiable fromoutside, have the NAT and routing set; what should i do this.
From internal network works excellent…What have i mistake? Can anyone help mee?