Ubuntu Server Edition is meant to run on any Intel or AMD x86, AMD_64, EM_64T processors as well as Sun Sparc T1 processors. It requires a minimum of 128Mb of RAM and 1Gb of disk space. Depending on your needs, you might manage with less than this. However, most users risk being frustrated if they ignore these suggestions.
As a server LTS, 8.04 benefits of 5 year lifecycle.
The following is a selection of some common packages packages that are fully maintained on Ubuntu Server Edition.
Default 2.6.24-server Tickless, No Preemption, Deadline I/O, PAE, 100Hz
JeOS 2.6.24-virtual Stripped down kernel for Virtualization
Apache 2.2 event/prefork/worker/dev
Full up to date list of packages, sorted by release and categories can be found at http://packages.ubuntu.com/