I've got apache-1.3 and thttpd-2 installed on my redhat 9 server.
Now if i do an 'apt-get upgrade' or 'apt-get install ...' i get the following error:

You might want to run `apt-get -f install' to correct these:
The following packages have unmet dependencies:
apache: Conflicts: thttpd but 2.23beta1-2.fr is to be installed

Can i let apt-get ignore this by editing /etc/apt/apt.conf ???

what happens when you type apt-get -f install?

I also see you are installing thttpd-2 when you have thttpd already installed. Perhaps apt-get remove thttpd

apt-get -f doesn't work. It wants to remove thttpd, while i need both apache and thttpd on my server.

[root@lnxsrvr root]# apt-get -f install
Reading Package Lists... Done
Building Dependency Tree... Done
Correcting dependencies... Done
The following packages will be REMOVED:
thttpd
0 packages upgraded, 0 newly installed, 1 removed and 0 not upgraded.
Need to get 0B of archives.
After unpacking 1873kB disk space will be freed.
Do you want to continue? [Y/n]


I think that there should be an option in /etc/apt/apt.conf to ignore this, but i'm not sure.

It looks like thttpd and apache aren't playing nice. One option would be to go ahead let thttpd to upgrade like it claims it wants to.
dpkg -i --force-conflicts /var/cache/apt/archives/thttpd-2.23beta1-2.fr.deb

I can't test myself this so some syntax might be off.

does dpkg work if i'm using redhat?
I thought it would only work with debian?

It will work since you're using apt-get, and apt-get is just a frontend to dpkg.

<edit>
After googling a bit, I see that a redhat apt-get uses rpm instead of dpkg. I'm afraid I don't know much about rpm, but maybe there is an equivilent option to what I said before. Sorry for the confusion.