today i receive a pm about the same problem so This is how i fixed the problem without using ntlmaps
Yes I solved that problem by Installing DNS server on win 2k3 machine with ISA server... In the wizard when installing DNS server in 'Forward Lookup Zones' Give the ip of linux box you can also add ip after installing dns server as shown in the pic. In this case 192.168.0.123 and 192.168.0.125 are ips of linux box.
After doing that DNS stuff open ISA Server MMC go to 'Array>>Configuration>>Networks and double click Internal network in popup window under webbrowser tab add the ips of linux box as shown in pic.
This is what i've done to access internet on linux box through ISA firewall, Hope this help, Do tell me if it works for you.
Also note that when using forwarders ISA server Cache will not work.. All your requests will be forwarded to the isp. Also on linux box in network settings give ISA server IP in DNS and default gateway.
Now every software will work without proxy (direct connection).