New system build

Ok so im going to replace my old system now

amd xp 2200+
Geforce 6600 256mb
1.5 gb samsung pc2700


it is actually surprising that it's been serving me for that long, but this tuesday it will change as i will go and buy a new one. What i am sure of already is that i want a 24" monitor and i thought i would feed it with a 4870 card. (no money for a bigger right now)
Im then going for the e8400 processer.
The thing is i want to be able to overclock it to 4ghz and with the option to go higher.
So my questions are:

1. what motherbord should i get, also considering things like a bigger cpu cooler not blocking a memory slot f.ex

2.what memory?

3.thinking of a 500mb hd that i could later replace with a 10000rpm of some kind. but which 500mb should i pick?

As you may have noticed i might be a bit outdated in my PC knowledge, so i hope you can assist me in choosing those parts.

thanks for your time