Small / Cheap desktop

Hello,

I am planning on building my mum a new pc as hers is getting on a bit and was wondering if anyone could give me a couple of pointers.

It doesn't need to be overly powerfull just enough for email, browsing and letters so onboard sound and graphics would be fine and she already has keyboard, mouse and monitor.

I was planning on something like this:

Athlon XP 2100 (already have this)
256MB ram
40 Gb HD
56k PCI modem (already have this)
Probably Asus A7N266-VM/SE or Asus A7N8X-VM nForce2 MB if not going the Shuttle route

My dilemma is what sort of case to get, it has to be a desktop case as there is no space under the desk but I was hoping to get something a little smaller than a standard desktop.

So far I have looked at a Shuttle, the Antec Minuet case and a Revolver case from Ebuyer (QF 52931).

The problem is only the Shuttle will take the full height pci modem but it is by far the most expensive and I am not sure if it is suitable for standing a 15" CRT monitor on top of (the monitor is too low just resting on the desk).

I would be happy to buy a half height pci modem if neccesary but cannot find anywhere that sells them - does anyone know of anywhere? Or can I just buy a new hanger to go on the exisiting modem - it looks pretty small?

Finally - noise, I would like it to be as quiet as possibly (within reason) so a suitable cooler if not going the shuttle route might be usefull.

Many thanks for your help.