i don't know yet about the NAT & DNS things.
our admin is not around yet but what i know is
that a DHCP provides IP for the workstations.
i also tried ping & traceroute commands for our
proxy and got the ff:

PING:
knoppix@ttyp0[knoppix]$ ping 129.1.2.57
PING 129.1.2.57 (129.1.2.57): 56 data bytes
64 bytes from 129.1.2.57: icmp_seq=0 ttl=128 time=0.7 ms
64 bytes from 129.1.2.57: icmp_seq=1 ttl=128 time=0.3 ms
64 bytes from 129.1.2.57: icmp_seq=2 ttl=128 time=0.4 ms
64 bytes from 129.1.2.57: icmp_seq=3 ttl=128 time=0.4 ms
64 bytes from 129.1.2.57: icmp_seq=4 ttl=128 time=0.3 ms

--- 129.1.2.57 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 0.3/0.4/0.7 ms

TRACEROUTE:
knoppix@ttyp0[knoppix]$ traceroute 129.1.2.57
traceroute to 129.1.2.57 (129.1.2.57), 30 hops max, 38 byte packets
1 129.1.2.57 (129.1.2.57) 0.365 ms 0.308 ms 0.299 ms

thanks!