Low powered server?

Hey,

Need some advice, Currently in my house I have a main server PC which is left on 24/7, and it houses all of my videos, music and just about everything else for that matter!

Currently it is a P4 2.8ghz, Bioster G31 Mobo, 1GB Ram, 350w BeQuiet PSU, a 40gb IDE HDD (for the OS, which is XP) and a 1TB WD Green Drive for all the data.. However i've been thinking recently about trying to conserve energy and lower household bills..

After using this http://extreme.outervision.com/PSUEngine my system comes out at about 160w, which isn't terrible.. but isn't great by any means

So, I have been looking into building a lower power system which is both silent, cheap and small, but am unsure about which way to go..

I have looked at a mini-itx system based around the intel atom 330 and Gigabyte GC330UD board... http://www.ebuyer.com/product/167781

My main problem with this is that all of the mini-itx cases I can find (i'm UK based) only have enough room for 3.5" drive or 2.5" drives.. and considering my 1TB is nearly full and I want to add at least one more drive this doesn't seem a viable option?

So... My question is, can someone link recommend me or link me to a page which has a list of super duper low power cpu's; I basically want to try and keep my system wattage as low as possible

I am on a VERY tight budget, and I only need a new CPU+Mobo, it literally has to do nothing but turn on, serve data and then turn off... so it doesn't need to be great... oh and the mobo needs onboard GFX..

Can someone help out?

Alex.