@so19 it depends on how much visitors you have. In leechking.com case we have about 6k visitors and we will running on Pentium Dual Core, 2Gb of RAM 500Gb HDD (100Gb is enough) and 100mbps with unlimited BW (now we using ~700 Gb / day)

What can i say, for 6k visitors this is to low. We need 4+ RAM and 4+ core CPU. If you have 1gbps line then you will need HDD with RAID0 and 8 Core CPU.
Main problem is very high IO usage, so you need real fast HDD and lot of CPU.

Don't even think about Apache, best choise is Nginx, we using Lighttpd, because I'm not familiar with engine x.

Sorry for my BAD english hope you understand something.