Network Problems when installing Debian

Dear Freinds,

I am a newbie who just begin to learn using linux.
I have downloaded the newest version of debian and
tried several times to install it. But I always met
the same problem and don't know how to solve it.

I have a home net configured by a friend, who has
already left for a new city and can't help me now.
Any way, my other PC connecting to the server can
access the internet well.

I am sure the network card is installed well. I
can ping the gateway, the ip of which is 192.167.0.1.
I can ping the other Win2000 PC with ip 192.167.0.2.
I can even ping the outer ip of the gateway, which
was provided by the campus computer service. But
DNS servers' IP can't be accessed and further ...

What is confusing is that when I tried to get
security update from security.debian.org in the
installing process, it works very well. But after the
installation is done, it can't reach out any more.

I used "route" command to check, it reacts promptly
and gives the information.

Then I changed to Redhat 8.0. The same thing. Very
strange.

Thanks a lot for your kind help.

Best and Merry Christmas.
Haoyu