Extend my hard-wired LAN

I run a small WinXP Pro LAN at home.

This has two hubs and three PC`s. One of the hubs is in place simply to
extend a cable (it was a bodge at the time and never got rectified).

Anyway, I also connect my laptop to this set-up when I`m at home.

What I would like to do - as cheaply as possible - is incorporate a wireless
facility. I want the fastest option possible and the only PC using the
wireless link will be that laptop at the moment.

Also, the laptop has no PCMCIA port so the adapter here has to be USB.

So how do I do this ?

What do I need ?

Thanks in advance

MJ