If you mind to connect a Homematic CCU with a FHEM Server (e.g. running in a Raspberry Pi) you will have to do the following steps:

Via SSH:

sudo apt-get install libxml-simple-perl
raspberrypi /opt/fhem/contrib/HMRPC $ sudo apt-get install librpc-xml-perl
raspberrypi /opt/fhem/contrib/HMRPC $ cp *.pm /opt/fhem/FHEM/

On FHEM Web Interface:
Command Line:

shutdown restart

Problems

Here are some problems I ran into:

Unknown module HMRPC

Solution: move the modules to the right place.

raspberrypi /opt/fhem/contrib/HMRPC $ cp *.pm /opt/fhem/FHEM/

Invalid characters in name (not A-Za-z0-9.:_): homematic-ccu2

Solution:
Change name…

Can’t locate RPC/XML/Server.pm in @INC

If you receive that error:

Server started with 9 defined entities (version $Id: fhem.pl 7124 2014-12-05 07:10:20Z rudolfkoenig $, os linux, user fhem, pid 7683)
2014.12.06 13:49:58 1: reload: Error:Modul 00_HMRPC deactivated:
 Can't locate RPC/XML/Server.pm in @INC (@INC contains: /etc/perl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/local/lib/site_perl . ./FHEM) at ./FHEM/00_HMRPC.pm line 24.
BEGIN failed--compilation aborted at ./FHEM/00_HMRPC.pm line 24.

2014.12.06 13:49:58 0: Can't locate RPC/XML/Server.pm in @INC (@INC contains: /etc/perl /usr/local/lib/perl/5.14.2 /usr/local/share/perl/5.14.2 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.14 /usr/share/perl/5.14 /usr/local/lib/site_perl . ./FHEM) at ./FHEM/00_HMRPC.pm line 24.
BEGIN failed--compilation aborted at ./FHEM/00_HMRPC.pm line 24.

You may have not installed:

raspberrypi /opt/fhem/contrib/HMRPC $ sudo apt-get install librpc-xml-perl