Stoney X,
I just had to comment, having worked extensively with datacentre servers, particularly rack-mounted Compaq Proliants, but I also have a lot of experience with HP, Dell and IBM kit.
They are VERY noisy in comparison to your average desktop. Multiple power supply fans, cooling fans and disks make a hell of a racket.
They do consume much more power than a desktop (3 or 4 times, depending on the configuration).
They don't mind being powered up and down at all. It is the hard disks that don't enjoy being spun up and down, but no more so than any hard disk on any computer. Servers are just glorified PCs with built-in resilience features.
Running one such server in a reasonably well ventilated room would not be a problem regarding cooling. it is only when you are running several, plus disk enclosures, screens, peripherals and comms kit that you start getting into overheating problems without installing air con.
But what on earth would you want to DO with it that you couldn't accomplish with a bog-standard desktop / minitower? The advantage of a Server as opposed to a PC is simply one of fault tolerance. Use them where you need high (ish) availability and reliability, with fewer single points of failure.
You can run server operating systems (all MS Windows, from 3.5 thru 2000, I haven't tried 2003) perfectly well on PCs (and vice-versa, but why?). You can add a SATA or SCSI RAID controller and multiple NICs to a desktop PC - what's the difference, except for hot-plug / redundancy / resilience / fault-tolerance?
Multiple processors are only of value where you have an O/S and / or application that can take advantage of them, and that will be stressed to the point of needing to use them. Databases and OLTP servers spring to mind. Again, you can run desktops with 2 or more processors - great for compute-intensive applications, not for most end-user tasks.
Sorry if you know all this, but from your original question I assume that you don't!
SD