laptop wifi on a desktop?

quick dilemma:
my mothers laptop here gets internet access from a wifi hotspot she connects to... she cancelled our dsl because she gets her internet from her wifi and my brother said he is gonna get a wifi card for his desktop... my desktop has linux (fedora core 5) and a standard NIC with the RJ45 on the back...
my question:
is it possible to jack into the back of my brothers desktop or moms laptop from my desktop or something like that and get internet restored to my linux? or do i have to go out and get one of those wifi cards too?

Hi,

You could set up a network bridge on your brother's or mum's PC, if either of them had a standard ethernet card as well as wireless, but it would be just as easy to go out and buy a wifi adaptor for £20 ($25)!

James