Thats something i cant explain because its nothing to do with the source code other than its the main requirement that needs to be on the server, every os flavour is a different procedure, Your going to have to search for an install guide for your flavour IE Cent os, Debian, Unbuntu, Windows.. howtoforge have the best guides usually so just use google like all us guys do and see how you get on.
http://www.howtoforge.com/php_memcache_centos5.0
http://www.howtoforge.com/installing...n-etch-apache2
http://www.pcbg.co.za/threads/6769-H...ache-on-Ubuntu...
And thats just the first few that came back from google so you now know what you have to do.