your going to struggle to get a wireless dialup device. (modem)
If your get broadband it gets a whole lot easier.
you can find lots of kits on:
http://www.broadbandbuyer.co.uk (their nothing to do with me, but a good place to start)
I use a Netgear DG834gt - works a treat with both my Mac & Sazza's Windoze machine.
I'm a Apple Mac man myself, they do do a Wireless router with modem for around £140.
My advice - go broadband