First, decide if you need memcached. APC is both an "accelerator" (an opcode cache, which is fairly transparent), and a caching solution (provides an in-memory data store that code needs to write/read from). memcache only does the latter.
The only reason you'd typically need memcached is if you're going to be running multiple servers that need to read/write from the same cache. As long as you're only running a single web server host, APC will do the trick.
Installing APC is pretty easy.
[root@host]# pecl install apc #or sometimes pecl install apc-beta
[root@host]# service php5-fpm start
You'll probably notice an immediate performance boost, just with APC's default settings.
You can then tweak as needed. See the docs for various settings.
The most common setup I've seen is a single segment, sized in a way that makes sense for your system:
In php.ini:
extension=apc.so
apc.enabled = 1
apc.shm_segments = 1
apc.shm_size = 50M
APC comes with a handy apc.php script that will give you lots of useful data (like how many hits/misses you're getting), along with pretty graphs.
The latest version of SUSE should have PHP 5.3 by default, however maybe you're running an older version?
If so, you'd probably be best off compiling from source. Get the download from here and follow the instructions on how to compile and install.
Best Answer
you need to install
php5-devel