I recently wanted something similar but rather be limited to just storage I bought a cheap mini-itx PC off ebay and put a linux OS on it. It is now hooked up to my network and I can access the files from any PC/mobile phone/PS3 from anywhere in the house. Transfer speeds over wireless aren't brilliant, but it only cost me about £70 and I can access the case to add and remove hard drives as I like. Next plan is to add a 1TB drive for about £60 bringing the total cost to £130. Cheap cheap compared to a dedicated NAS and is able to do a lot more.

NAS storage device is what you're looking for, although a NAS box that isn't sealed (ie: where you can change/add drives) tend to be fairly expensive (£200+) - but have a look at the Drobo, QNap and Lacie boxes (although i think Iomega, Netgear and Buffalo also dude non-sealed units). It might be the case of looking at some reviews for devices though :thumbs:

edit - oh, and although you can get NAS boxes with built in wireless majority tend (and the prefered method of connection) to have a ethernet port on them so the NAS box needs to be positioned near the router. And setups of NAS boxes tend to be fairly straight forward, have a web interface similar to a router etc.

[Edited on 08-08-2009 by Dom]

in my house we have a couple of desktops and a couple of laptops what i want is a harddrive that shows on the wireless network that i could dump some of the files on maybe drag and drop music there and games so that you can use then from anywhere in the house...would like something with at least 1tb of space but preferably can add additional drives to