First check the specs for this computer -- most new ones include wireless as standard. If it's not working check whether there's a switch or Fn key combination required (see manual which may be on CD that came with computer or on Toshiba website))
No-- okay, check the hatches underneath for what's called a mini-PCI socket
illustration is a little way down this wiki page:
http://en.wikipedia.org/wiki/Conventional_PCI
I would advise buying exactly the model of adapter normally installed, some brands of laptop are very fussy about what you attach.
Alternatively buy a USB or PCMCIA type wireless adapter.