WiFi network possibilities

I'm curious how to enable a wifi connection to a PC desktop setup that has a unique DSL connection (Not a typical router).

Basically, I want to be able to connect to this desktop PC that is wired to the DSL connection through a laptop...Is that possible without purchasing a special kind of router?

Can I add some sort of wifi card or something for the PC that will broadcast the internet connection to connect via wifi on my notebook?

Thanks