What can I use a Home server for?

Sorry for the really nooby question but my bros happen to have spare computer components lying around and I've been constantly asking them If I could use the parts but they don't wont to use the parts on a server they insist that they can find some other use such as a backup computer.

I've been constantly "amping" up the uses of building a home server, they seem interested but I can't seem to persuade them due to me not having a lot of knowledge about servers and what they are used for..

I know a little about them, but since I've gained this interest in them I've been constantly studying them so my knowledge of them is expanding.
There happens to be a spare computer case which I used to own but due to it's one fan I removed my computer from It because It was practically an oven, I intend on having a 24/7 server but what are It's major uses?

I know you can stream movies and music from them, I'm pretty sure you can do file transfers also but I'm not entirely sure how effective file transferring from a server Is can can be, I like fast transfer speeds but how can an old IDE drive measure up to the task and perform effectively?
There's a lot of IDE drives hanging around that are slowly rotting away in Anti-static bags, I hate seeing them around because they are just becoming a waste of space and they can be put to some good use, especially in a home server.

Servers are mainly;y used for Data transfer such as websites and game servers, I used to play Mine craft but I've become increasing distracted and a bit busy, but I'd defiantly enjoy running a server for a few of my friends since I have decent internet speed and I've done it before but running on my own computer, If I was to make a server I would enjoy It's multiple uses, a Mine Craft server, data streaming, file transfers and the occasional backup.
But is there anything I've missed and what are good components to use for a little home server for friends and family?

I've glimpsed a few IDE drives around.
And a DDR2 motherboard with about 8GB of ram.
I know of two spare Core 2 Duo Dual core processors.
And an oven! no wait I mean a PC case..

Any help and suggestions would be greatly appreciated!

Whoa, It looks like I'm gonna have to invest some serious time and money into making a home server.
All I really have is blueprints to a desktop computer really I was thinking of running a linux or windows server.

I have O2 internet with about 12mbps down speed and 1mbps upload speed, upload speed is vital for transfers, I may considering getting a different ISP, but I don't wish to spend a lot of money on internet speed, no matter how valuable the internet is does the router I use affect the speed also?

When I download stuff from steam I download about 1.3MB/s - 1.4MB/s when speed test says 12mbps, I heard that MB/s and mbps are different but I'm not entirely sure. and when uploading to you tube It's about 900kb/s.

I just want a basic server, data transfer, data streaming, maybe a website and hosting a mine craft server, I don't think I have sufficient internet speed to do all of this, my MC server ran well but ate a lot of Up speed, It didn't really download a lot but I can't recollect the numbers.

Wow the more I hear about home servers makes me want one even more! But what are NICs for are they easy to integrate into the server and setup?
Also is it possible to connect to the server safely from a different place? I'm not talking about the Minecraft server I mean if I go on holiday or something and I wish to obtain or stream files from the server while I'm somewhere else?