I was surprised to see Ettercap is not in the OSS repo nor a few others I use. I am sure its in a Suse 11 repo somewhere, but its easy enough to install.
I noticed it has a few dependencies though, and that might through a curve so I thought I would describe some solutions.
First, get the RPM for ettercap, I used RPM Search but any good RPM library site should work. I like this one as you can search easily by distro and version. I searched and found an ettercap RPM for Suse 10. Find a similar RPM and wget it:
Using rpm -ivh ettercap-NG-0.7.3-1.i686.rpm will give some dependency errors. You can install each of them if you like, but there is an easier way:
Install the yum package manager as this will allow you to install local RPMs and handle the dependencies, something zypper (unfortunately) does not do. In addition to yum, you will also need to install yum-utils which adds the local installation feature to yum. Install both at once with:
zypper install yum yum-utils
Now, you can use yum to install the rpm, and resolve any dependencies with:
yum localinstall ettercap-NG-0.7.3-1.i686.rpm
Tada! Pretty nifty eh?
(You can also use the "smart" package manager in Suse instead of installing yum, it can also install a local file and resolve dependencies. Either way, both will get the job done.)
If you get a gpg signature error, then install the appropriate gpg key, which (in an ideal world) should be available from where you got the RPM from. If you can't resolve this, and you trust the source of the RPM, you can temporarily disable GPGCheck in /etc/yum/yum.conf However definitely reactivate this after installing, you don't want to leave this off.
For more info on GPG keys and package managers you might find the following useful:
Gpg Keys for Package Validation - Lyceum
Linux Package Managers - Lyceum
You now have yum installed - it uses it's own repos which can be found at /etc/yum/repos.d and should you need to resolve dependencies when installing future RPMs this might greatly assist.
Have fun with Ettercap!