cant't upgrade libc6 using atp-get

[Johann Kallinovsky <j.kallinovsky@1012surfnet.at>]

I have Debian 2.0 installed.
I want to upgrade to 2.1.

I'm using apt 0.3.4.

I did copy all the files from my Debian-2.1-CDs onto my harddisc and edited
sources.list accordingly -> It seems to work.

When I want to upgrade some package e.g. wwwoffle:
# apt-get -f -s install wwwoffle
Sorry, but the follwing packages have unmet dependecies:
  wwwoffle: Depends libc6 (>= 2.0.7u) but 2.0.7t-1 is installed.

OK, this is normal.
So I tried to upgrade libc6:
# apt-get -f -s install libc6
Sorry, libc6 is already the newest version.

BUT: On my Debian-2.1-CDs is libc6_2.0.7.19981211-6.deb which IS newer than 
version 2.0.7t-1 ans which is also newer than version 2.0.7u (This is written
in the changelog.debian of this package)

1st question: Any clues what to do?

2nd question: In the changelog.debian is also written:
...
glibc (2.0.7u-2):
... as this version is not backward compatible with earlier versions.

-> When I upgrade to libc6_2.0.7.19981211-6, will this break other installed
packages, or is it safe to do this upgrade?

Many thanks in advance
Johann Kallinovsky (Austria)