Beste Rien,
I have installed wiki and the latest version 1.7 and above requires PHP 5, but as you proved SME 7.0 is not ready for installation yet since work needs to be done on Horde.
Since I expected some problems I didn't want to install PHP 5 because if you modify the core system too much I expect future problems with updating aswell.
But let's have a look at some possibilities
I had a quick look at the horde site and the IMP package requires php 4.3.0 no words mentioned about PHP 5 yet. So a quick download of some php 5 compatible version of IMP is out of the question.
Let's have a look at PHP itself then:
If I give the following command in my shell (standard installation)
yum list installed php-*
Installed Packages
php.i386 4.3.9-3.12 installed
php-domxml.i386 4.3.9-3.12 installed
php-gd.i386 4.3.9-3.12 installed
php-imap.i386 4.3.9-3.12 installed
php-ldap.i386 4.3.9-3.12 installed
php-mbstring.i386 4.3.9-3.12 installed
php-mysql.i386 4.3.9-3.12 installed
php-pear.i386 4.3.9-3.12 installed
If you give this command you probably miss php-domxml, so we have to look either for a Centos or a Fedore rpm for installation. Please sent the output of your sme7.0 php 5 machine.
What will the following commands do on you machine? Please sent output
yum --enablerepo=centosplus install php-xml
Maybe it does do the trick and install both the xml and the dom modules?