Grant, you'll need something like this. I recommended the 3com ones to some people at work as I'm currently using one of their access points at home with great success, and I never got any complaints.
I personally hook up 2 laptops, a Nintendo DS, a PSP and my new MDA Vario Phone to my Wireless. My xbox, xbox 360, PS2 and Cube are all cabled up, as is most of my other PCs though.
Other than that you'd just need a bit of cable to connect to your mum's PC to the router and you're quids in.
I don't know if the other guys have any recomendations for cable routers or have any cheap ones going spare. Most stuff I've dabled in has been ADSL based.